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 th............