introduction: the blowpipe.

it is not our intention to write an elementary treatise on chemistry; but we know it is the custom for brickmakers to have chemical analyses of their raw earths made, and we are aware also that the precise meaning to be attached to these analyses is very little understood. our principal aim in introducing this subject, then, is to interpret, in an elementary manner, certain typical analyses of earths and substances used in brickmaking; but before doing so we shall explain some easy methods of examining earths by means of the blowpipe, which will not merely give some insight into their chemical constitution, but will afford the intelligent brickmaker a means of investigation which he can himself put into practice.

the results of a chemical analysis of a compound earth, as ordinarily used by the brickmaker, widely differ from those obtained by a mineralogical or petrological examination. the petrologist views the earth as a mineral aggregate, the constituents of which may be ascertained on appeal to a properly-constructed microscope—that is, in the majority of instances. by noting the relative proportions of the different minerals, he is enabled to state, with approximate accuracy, what is the ultimate chemical composition of the whole. from this it would appear that a rough chemical analysis could be drawn up by the petrologist without having recourse to the ordinary methods of chemical investigation. and in a59 limited sense that is true. but we should not lose sight of the fact that there is, in too many cases, an amorphous residuum in earths, the nature whereof the microscope is powerless to reveal. it is upon this remnant that the chemist should direct his most careful attention.

the mineralogist also can give a shrewd idea of the chemical composition of a brick-earth by using a blowpipe and accessories. this, in fact, may be regarded as a chemical means of investigation; but it possesses this serious drawback, viz., the blowpipe only yields a qualitative, and not a quantitative analysis. in other words, it can tell us something concerning chemical compounds present in an earth, but rarely informs us as to the relative proportions of them. even this, however, is of great service in many instances, though it does not possess the value of a quantitative analysis. for example, we have stated previously that certain ingredients are very undesirable in a brick-earth, even in minute quantities; and that fact becomes of increased value if we extend the field to earths used in terra-cotta, and china and porcelain manufacture. now, the blowpipe is a handy instrument; it may be carried about by the prospector with its usual accessories, and occupies but little space. suppose he discovers a bed of white earth which he believes to be good china-clay; he can prove that fact, or at least obtain a great deal of information to that end, by the mere use of that useful little instrument. knowing, for example, that fluorine is an undesirable constituent in such a clay for many high-class purposes, he might test first of all for that; iron, perhaps, may come next, and so in a few minutes he is enabled to arrive at some valuable particulars that would take much longer to obtain by chemistry in the wet way.

60 it will be profitable, therefore, for us to briefly describe the blowpipe and the most common of its accessories, stating results obtained in dealing with substances frequently met with in brick-earths. with but little practice anyone can use the instrument, though, as with most other methods of scientific investigation, it requires expert knowledge to yield really excellent results. the simple minerals and compounds to which we shall direct attention may be detected with the greatest ease.

the essential constituents of a blowpipe outfit are as follow:—

1. blowpipe.

2. lamp.

3. platinum-pointed forceps.

4. platinum wire.

5. charcoal.

6. glass tubes.

7. chemical reagents.

8. miscellaneous articles.

fig. 5.—blowpipes.

1. the blowpipe.—common forms of blowpipe are shown in fig. 5. a may be described as follows. it consists of three separate parts: a tube a b having a mouthpiece; an air chamber c to retain moisture caused by the breath of the person blowing; and a side tube d ending in a platinum-tipped jet. another form of blowpipe, which,61 however, does not differ essentially from that just alluded to, is shown in fig. 5, b. it is not absolutely necessary to have the jet made of or tipped with platinum, though certain examinations with the instrument are facilitated by the use of such a tip. an essential point is, that the hole in the jet should be of proper size, usually about 0.4 mm. the trumpet-shaped mouthpiece shown in the diagram may be dispensed with.

fig. 6.—blowpipe lamp, &c.

2. the lamp, or candle.—a convenient form of lamp is a bunsen gas-burner furnished with a special jet (fig. 6, a). for certain purposes, however, this flame cannot be employed, as when testing a substance for sulphur, as coal-gas frequently contains sufficient sulphur to vitiate results. moreover, in country districts and in the field coal-gas is not always procurable. a convenient form of lamp, though rather too large for transporting purposes, is known as berzelius’ blowpipe lamp. this, as improved by plattner, is shown in fig. 6 b. this consists of an oil vessel on a stand provided with two openings closed with screw-caps, the one opening being used for charging the lamp with oil, the other being fitted with a burner bearing a flat wick.62 the lamp may be adjusted to any required height on the stand by means of a screw. olive oil, or refined rape oil, is usually burnt. a spirit lamp with a flat wick is sometimes used. in countries where neither coal-gas, alcohol, nor oil are readily available, the prospector may use a small grease lamp. this consists of a cylindrical box of thin metal having a wick-holder soldered on one side, through which a flattened wick is drawn. the box may then be filled with grease, solid paraffin, old candle-ends, or fat of similar description. professor cole describes6 it as follows:—when brought into use the wick is lighted, and the flame directed with the blowpipe upon the surface of the solid tallow or fat, until this is melted to a depth of about a quarter of an inch. the lamp will then become hot enough during use for a continuous supply to be maintained; but it is still better to hold the lamp with the pliers over a spirit lamp until all the contents become fluid. when about half or three-quarters empty, it is well to drop in extra lumps of fuel—a single candle-end or so—during use, and this additional material becomes melted up slowly with the rest. the wick must be freely supplied with fluid fuel, or it will char and waste away. if the lamp is kept sufficiently hot, the wick will not require raising during a day’s work; but it can be easily thrust up with a knife point after the flame has been at work a few minutes. a cylindrical cap fits down upon the lamp when put aside. for many ordinary purposes a good carriage-candle may be employed to give a blowpipe flame, but candles have the disadvantage of not remaining at a constant level—an important point when one is comfortably at work.

633. platinum-pointed forceps.—at least one pair of forceps is needed, and it should preferably be made of steel, nickel-plated to prevent rusting. one end has platinum points self-closing by means of a spring, so that the piece of mineral to be heated, placed between them, may be firmly supported. at the other end are other forceps of ordinary pattern for picking up small fragments; this end, however, should never be placed in the flame. a pair of common self-closing forceps might also be at hand for holding test-tubes, etc., in the flame.

4. platinum wire.—a few inches of thin platinum wire are indispensable, and lengths of an inch or so may be fixed into suitable handles. a convenient method is to have a small glass rod for a handle, and by fusing the tip of one end of the rod the glass may readily be made to hold the piece of wire. pieces of platinum foil are useful, also, as will presently be seen.

5. charcoal.—the outfit should comprise several pieces of charcoal, and a convenient form for each piece is a circular disc about an inch in diameter, flat at the top and convex beneath. long prisms of the same material, square in section, are occasionally required; these may be up to 6 inches, or so, in length.

6. glass tubes.—these should be of hard glass, small, of several diameters, the bore being large enough to place fragments of minerals or earthy substances within. closed tubes, such as test-tubes, are always requisite.

7. chemical reagents.—these are, for the most part, used as fluxes, and those most commonly employed are borax (sodium tetraborate), soda (sodium carbonate), and salt of phosphorus or microcosmic salt (phosphate of soda and ammonia). small quantities of potassium bisulphate (in a glass bottle), as also small bottles of64 hydrochloric, nitric, and sulphuric acids, and a solution of cobalt nitrate, are also useful in certain cases. it is hardly necessary to remark that the chemicals employed must be of the highest degree of purity.

8. miscellaneous articles.—strips of test paper, both turmeric and blue litmus, a small hammer, a steel anvil about an inch cube, a bar magnet, a pair of cutting pliers, a three-cornered file, and a few small watch-glasses are very desirable, though not absolutely essential.

the reader, on glancing at the foregoing formidable list of articles, may possibly imagine that some considerable outlay is requisite, and that they must occupy much space. but that is not the case. an ordinary blowpipe, a grease lamp, a small spirit lamp, and all the articles mentioned in paragraphs 3 to 8, both inclusive, occupy but a small space. they may be packed in a box specially fitted, and one in the writer’s possession, containing all of them, measures only 10 inches by 5 inches by 3? inches, and is less than 3 lbs. in weight.

now, as to the use of these various things. first of all, let us examine the flame, as produced by a candle, which is typical of flames obtained by other means described, except the bunsen lamp. a candle flame (see fig. 7) consists of the following parts:—

1. a dark core (a), which contains the gaseous products of decomposition given off by the melted tallow drawn up by the wick.

2. a highly luminous zone (b), in which only partial burning of the combustible gases takes place. in this, oxygen from the air combines chiefly with the combustible hydrogen, whilst the carbon is separated in a highly heated state, which causes the luminosity.

3. an outer mantle of blue tint (c), where the oxygen65 of the air is always present in excess, so that the separated carbon is here burnt. the highest temperature is found in this part of the flame.

fig. 7.—candle and gas flames.

technically, the outermost zone (c) is known as the oxidising flame, and the inner luminous zone (b) the reducing flame. the two portions of the candle flame act in different manners on specific mineral substances, and the blowpipe operator may use either of them at will. the method of doing this is illustrated in the same figure. to obtain the reducing flame, the blowpipe jet is brought to the edge of the flame a little distance above the burner, or wick. the operator then produces a gentle blast, which deflects the latter (upper figure) without altogether passing into it, so that the flame is still charged with glowing carbon. a yellowish luminous flame is the result, the most active part of which lies at a short distance from the end.

on the other hand, the oxidising flame is utilised by passing the blowpipe jet a little farther into the flame (lower figure) and blowing more strongly. a pointed non-luminous flame is the result. this will be seen to possess66 an inner blue cone, before the point of which the hottest part is situated. substances to be fused are placed in this part of the flame, whilst those to be oxidised are placed a little farther away, in order that they may be exposed to the air at the time they are being highly heated.

the “platinum wire” is an absolutely indispensable adjunct to a blowpipe outfit, and is employed as follows:—a short piece of the wire, an inch or so in length, being attached to a handle, as previously described, the free end of it is bent into a loop about the size of this o. this may be heated in the flame employed, or, better still, in the flame of a spirit lamp, and, when hot enough, it may be dipped into a small quantity of the powdered borax or microcosmic salt, some of which will be found to adhere to the wire. on further heating the borax it will swell out and form a number of irregular bubbles, which (heat still being applied) will subsequently settle down into a clear, colourless bead in the loop of the platinum wire. a satisfactory bead having now been made, a portion of the mineral substance to be analysed (in the shape of small grains) is taken up by dipping the heated borax bead therein.

the actual operation of determining the nature of the substance then commences. using the blowpipe, and directing either the reducing flame (r.f.), or the oxidising flame (o.f.), on to the substance on the borax, according to circumstances presently to be detailed, the operator notes the change in colour (if any) of the flame yielded by the process. at this point a very annoying thing sometimes happens; for, in liquefying the borax bead, it is apt to fall off the wire, and another bead has then to be made. to avoid this, great care should be taken not to blow too vigorously at first. with the67 microcosmic salt especial care and dexterity must be exercised in this connection. if all goes well, the powdered mineral substance (if fusible in the borax) readily melts down, and becomes incorporated with the borax. on permitting the latter to cool, which it very rapidly does, the bead should now be carefully examined, and any change in tint noted. most beautiful transparent colours, pregnant with meaning, are often seen to have formed with the borax as flux.

the operator may test his skill by making the following brilliant experiments. take up a few small fragments of the mineral malachite (a carbonate of copper) by means of the clear, colourless, heated borax bead, and then introduce them to the oxidising flame. they slowly dissolve in the borax, and, whilst doing so, the tip of the blowpipe flame becomes emerald-green in colour. after applying this flame for a minute or two, the whole of the mineral will have become incorporated with the borax, and, when the bead is still hot, note that it is also of a rich green tint, but that, on cooling, it turns blue. if too much malachite has been taken up in the first instance, a very dark green tint is imparted, which still remains when the bead is cold, and it appears to be quite black. its true colour, however, may be ascertained by flattening the bead out before it is quite cold. it is always well to begin by using a small quantity of the mineral substance at first, and adding to this as may be required.

assuming that a fine rich green bead has been produced, and that it contains a relatively large amount of copper, the operator may now hold it in the reducing flame and re-melt the bead; if the operation has been conducted carefully, the bead will then show red, and be practically opaque when cold. the red bead may now68 be re-heated in the oxidising flame, when it will be found once more to return to a green colour. the student will find this easy operation excellent practice, as proving to him, in the absence of a demonstrator, that he is really able to recognise and use the oxidising and reducing flames at will. many mineral substances yield a distinctive colour in this way—a useful factor in a qualitative analysis.

before using the platinum wire, be careful to ascertain that it is quite clean; a borax bead made thereon should be perfectly white and transparent.

the “platinum foil” is employed as a support during fusions; pieces about an inch and a half long, by half an inch in width, are generally used. a small platinum spoon is sometimes adopted when fusing substances with acid, potassium, sulphate, or nitre.

minerals may be tested to see whether, in the ordinary blowpipe flame, they are fusible or not. to do this, a fragment of the substance to be tested is held in the flame by means of the “platinum-pointed forceps.” if the mineral is found to be fusible, then its “degree of fusibility” may be ascertained according to the following table. the “degrees of fusibility” are six in number:—

1. fusible in ordinary gasflame, even in large fragments. example: stibnite, or grey antimony.

2. fusible in fine, thin pieces, in the ordinary gasflame, and in larger fragments in the blowpipe-flame. example: natrolite, a hydrous silicate of alumina and soda.

3. if very thin splinters be used, fusible without difficulty with the blowpipe-flame. example: almandite, or iron-alumina-garnet.

69 4. in thin splinters fusible to a globule. example: actinolite, a non-aluminous variety of hornblende.

5. thin edges may be fused and rounded without great difficulty. example: orthoclase felspar—already described.

6. fusible with great difficulty on the finest edges. example: bronzite, one of the augite group of minerals.

now, it is highly probable that many of our readers will not understand, or be able to recognise the six minerals above enumerated; and we recommend those who may be sufficiently interested, to purchase them from a mineral dealer—such as damon, of weymouth, or russell, or gregory, or henson, or butler, in london. a set, comprising the six, should cost from two to three shillings. with these, as a standard for comparison, the operator readily grasps the method of assigning a fusible mineral to its proper degree in the scale.

another object of examination in the forceps is to see what colour (if any) is imparted to the flame by the divers minerals experimented upon. it is a good rule not to permit the specimen, when being fused, to touch the forceps in the neighbourhood of the actual part fused. for a mineral containing antimony or arsenic would tend to form a fusible alloy with the platinum points, and so ruin the forceps.

the pieces of “charcoal” alluded to in our inventory, are used for placing the mineral substance upon in certain parts of the blowpipe operation, which may be briefly described. essentially the charcoal forms a support to the substance during fusion; but the glowing carbon has also a kind of reducing effect. taking a long prism of charcoal, such as that described, page 6370 ante, the mineral to be dealt with should be placed near one end of a flat surface and the prism so held that the flame from the blowpipe, will sweep down its full length. the object of so doing is to give a chance to any volatile substance (derived by the operation from the mineral) to deposit on the comparatively cool surface, which deposit is often indicative of the chemical nature of the mineral. to carry this point home, the following experiments may be conducted by the student. taking a piece of stibnite (sulphide of antimony), which, as we have just learnt, is a most fusible mineral, we place it on the charcoal in the manner indicated. whilst melting, and the blowpipe flame be continued to be directed upon it after it has become fused, it will be noticed that a yellowish-white deposit is taking place on the length of charcoal; this is called a sublimate.

mineral substances may also be assisted in fusing on the charcoal by using the reagents described in our list of chemicals, &c., included in a blowpipe set.

in regard to the use of the “glass tubes,” it may be remarked that they are used principally for the examination of minerals which yield a volatile substance on being heated therein, and to detect the presence of water and the like. it is important to make a distinction between the closed and the open tubes. when a mineral fragment is placed in a tube, closed at one end, whatever takes place will be in presence of very little air, or oxygen; on the other hand, when the tube is open at both ends, and is inclined during the experiment, a constant stream of oxygen passes through the tube, and the mineral is being dealt with in presence of that. the employment of this oxygen makes a great deal of difference in the results obtained, as a few elementary71 experiments will show. if we place a piece of sulphur in a tube, closed at one end, and heat it gently, we notice that a yellow coating takes place inside the tube; but if we now employ a tube open at both ends and heat it very slowly indeed, we notice that the sulphur goes off as an invisible gas, and if the experiment has been properly conducted, there should hardly be a trace of the sulphur left on the glass. a number of experiments of a similar nature might be quoted, but enough has been said for the present to show the utility of the tubes.

the “chemical reagents” alluded to have already been sufficiently described to render any further discussion on them unnecessary for our immediate purpose.

in regard to the “miscellaneous articles” mentioned, it may be remarked that the test papers are employed in the detection of certain acids and bases; whilst a strip of brazil-wood paper is for the detection of fluorine. the hammer and anvil are for breaking the substance to be tested into small fragments; the magnet for withdrawing particles of iron from the pulverised material; the three-cornered file for assisting in determining the relative hardness of minerals, &c., &c.

in examining substances before the blowpipe, it is highly desirable that the various operations should be carried out in some definite order. the following has been found convenient:—

a. in a glass tube closed at one end.

b. in an open tube.

c. on charcoal.

d. with borax and microcosmic salt.

e. as to flame colouration.

f. with other reagents.

the size of the fragment to be dealt with in an examination, depends on circumstances, but for ordinary purposes72 a piece of the size of a small rabbit-shot will be found sufficient.

it is convenient in this place to describe a few chemical reactions without the use of the blowpipe; that will render the effects on certain minerals, presently to be mentioned, clearer to the reader.

in the first place it may be ascertained whether the mineral is soluble in water, and if so, to what extent. then as to whether it becomes soluble in certain acids, such as hydrochloric or nitric acid. the former acid is generally used, except for metallic sulphides, and those minerals containing heavy metals, such as lead, silver, &c.; the latter is employed for the exceptions named. several minerals, even when in a powdered state, are hardly, if at all, affected by acids. the results to be noted during the test with acids, commonly fall into the following three groups.7

a. the mineral may dissolve quietly with or without colouring the solution; this holds good, for example, with hematite (a variety of iron), also of many of the sulphates and phosphates.

b. there may be a bubbling off or effervescence of a gas, which gas is usually carbon dioxide; but may be hydrogen sulphide. chlorine may be liberated, or reddish fumes of nitrogen.

c. there may be separation of some insoluble substance as sulphur, silica, &c.

we will close this chapter by stating the behaviour under blowpipe examination of various minerals, given in preceding pages, as being common in clays and earths used in brickmaking:—

quartz.—this is infusible, and remains undissolved,73 even in a microcosmic salt bead; but it fuses readily with soda, on charcoal. in the flame it splinters into fragments, which fly off with great rapidity. it is soluble in hydrofluoric acid. flint, when pure, behaves in a similar manner.

orthoclase felspar.—fusibility, 5; flame colouration brilliant yellow, when much sodium is present; not decomposed by hydrochloric acid. it may be distinguished from other common felspars by its high degree of fusibility.

oligoclase felspar.—gives a sodium yellow flame; fusibility, 3.5; not decomposed by hydrochloric acid.

biotite mica.—with fluxes gives a strong iron reaction of yellowish red colour; decomposed in concentrated sulphuric acid, leaving a residue of siliceous matter.

muscovite mica.—when heated in a tube closed at one end, yields water which often gives fluorine reaction with brazil-wood test paper by colouring it straw-yellow; it is not decomposed by acids, and whitens and fuses only on thin edges.

kaolin.—is infusible; gives off water when heated in a closed tube; and with cobalt nitrate on charcoal, a fine alumina reaction is obtained.

aluminium.—on charcoal, this becomes blue with cobalt nitrate, though if the surface is fused the reaction is not so clear. prof. cole advises that the soda-residue be dissolved in dilute hydrochloric acid, then evaporated to dryness, re-dissolved in that acid water, filter off any silica, and neutralise with ammonia; alumina is precipitated together with any iron present. the precipitate, if white, or nearly so, may be tested with cobalt nitrate, and the result is a fine blue colour.

limonite iron.—fusibility about 5; yellow and reddish74 beads; water given off in closed tube; in reducing flame magnetic residue on charcoal; soluble in hydrochloric acid after a short time.

iron pyrites.—fusibility about 2; yellow and red beads; in closed tube yellow precipitate due to sulphur; magnetic after reduction on charcoal; insoluble in hydrochloric acid.

rock salt.—intense yellow sodium flame; fusibility about 1; microcosmic salt with copper oxide shows strong chlorine reaction—a fine blue flame surrounding the bead when re-introduced into the flame. it is soluble in water.

selenite (gypsum).—fusibility about 2.5; brilliant flame; in closed tube it becomes white and opaque and much water is given off; with soda, on charcoal, sulphur reactions are obtained; soluble in hydrochloric acid.

calcite (carbonate of lime).—flame glows very strongly; infusible; effervesces freely in cold hydrochloric acid.

dolomite.—flame, with hydrochloric acid, like calcite; infusible; effervesces in hot hydrochloric acid.

magnesite.—infusible; with cobalt nitrate a fair magnesia reaction on charcoal, i.e., turns into a dull pink; effervesces in hot hydrochloric acid.

manganese.—with borax in oxidising flame a red-violet bead is obtained, but with the reducing flame it is colourless.

the above are commonly met with in brick-earths; for other minerals and substances also found, the reader may be referred to special works dealing with blowpipe analysis.