SECTION I.

I. THE BLOWPIPE.

THIS instrument was long employed in the arts, before any one conceived the idea of applying it to chemical experiments, performed in what is called the dry way. BERGMAN tells us, that the first person who so used it was ANDREW VON SWAB, a Swedish Metallurgist, and Counsellor of the College of Mines, about the year 1733. He left no work on the subject, and it is unknown to what extent he carried the researches which he made with this instrument. CRONSTEDT, who laid the foundations of Mineralogy, and whose genius so outstripped the age in which he lived, used the Blowpipe to distinguish mineral substances from one another, by means of fusible reagents. From their action such modifications on the objects to which they were applied resulted, as led to some conclusions respecting their composition, and served as a basis for the classification he adopted. In his time the intercourse between men of science was by no means so open as at present; the discoveries of one man were seldom communicated to his fellow-laborers, and each pursued his researches with no other help than the experience of the generation which had passed away, and become in some measure public property. At such a period, CRONSTEDT carried the use of the Blowpipe to a degree of perfection, that can only result from persevering industry; but, as slight services in the cause of science were not as yet honored with general attention, he who at first was afraid to make himself known as the author of that system of Mineralogy which has perpetuated his memory, still less thought of describing in detail this new application of the Blowpipe, and the system he adopted. He only published such results of his experiments, as might serve to distinguish minerals from each other, by affording characters

peculiar to the different species. VON ENGESTRÖM, who published an English translation of CRONSTEDT's system in 1765, annexed to it a treatise on the Blowpipe, in which he particularly noticed the processes of the author, as well as the principal results of their application to the minerals then known. This treatise did not appear till 1770, and was translated and published in Swedish by RETZIUS, in 1773. It attracted the general attention of Chemists and Mineralogists to the use of this instrument; they, however, derived at first little other advantage from it, than as a means of ascertaining the fusibility of bodies, and occasionally their solubility in borax; for it was difficult to form a just estimate of its value, in consequence of the want of that skill in its application, which can alone be derived from patience and practice, together with a sufficient knowledge of the phenomena presented by the various substances used as fluxes; whilst the difficulties attending its use were sufficiently evident; and hence, everywhere but in Sweden, the art of the Blowpipe made little progress. As in other practical sciences, books alone are weak masters to make proficients; but they who had seen the manipulation of CRONSTEDT and VON ENGESTRÖM, learned to work like them, and transmitted their skill to their successors. BERGMAN went further than CRONSTEDT; he extended the use of the Blowpipe beyond the bounds of Mineralogy to the field of inorganic Chemistry; and in his hands it became an invaluable instrument for discovering very minute portions of metallic matter in analytical researches. His work De Tubo Ferruminatorio was first published at Vienna, in 1779. BERGMAN, on account of his health, was assisted in his experiments by GAHN, who particularly applied himself to the use of the Blowpipe in his mineralogical studies, in consequence of the readiness with which it affords decisive results. The operations which he performed under BERGMAN's inspection, who caused him to examine all the minerals then known, taught him how each conducts itself before the Blowpipe. Assisted by the experience which he thus acquired, he continued to employ the instrument in every kind of chemical and mineralogical inquiry; whence he attained such a degree of skill in its use, that by its means he could detect in any body the

presence of substances, which had escaped the most careful analysis conducted in the moist way. Thus when EKEBERG asked his opinion respecting the oxide of Tantalium, then recently discovered, and of which he sent him a small specimen, GAHN immediately found that it contained tin, although that metal does not exceed one per cent. Long before the question was started, whether the ashes of vegetals contained copper, BERZELIUS saw him many times extract, with the Blowpipe, from a quarter of a sheet of burnt paper, distinct particles of metallic copper. GAHN always travelled with his Blowpipe, and the continual use which he made of it led him to several improvements in its application; he examined a great number of reagents, in order to find new methods of arriving at the knowledge of certain substances, and the whole was imagined and executed with such sagacity and precision, that his results were entitled to the greatest confidence. He most readily and carefully instructed those who were desirous of information on the subject; but he never appears to have thought of publishing an account of his labors, nor has it been done by others. In all the rest of Europe, only one distinguished Naturalist applied himself to the study of the Blowpipe and its uses, and submitted a large number of mineral substances to its action. This was SAUSSURE, justly celebrated for his geognostic researches on the Alps of Switzerland. He, as well as CRONSTEDT, employed the Blowpipe chiefly in distinguishing minerals; and although he made additions and improvements on the subject, he ranks far behind GAHN in respect to the results which he obtained.

The science of the Blowpipe, like all others, still continues to unfold new secrets, and offers more beautiful advantages in the way of analysis; for the use of this instrument is not confined to the detection of metals in minerals only, but by its aid the per centage of many of these, especially the precious ones, may be ascertained with surprising accuracy. HARKORT was the first to draw attention to this course of metallurgic determinations; he published the result of his labors in 1827, but it is to the diligence and ingenuity of the German author of this dissertation that the quantitative determinations by the Blowpipe owe their great exactness and simplicity.

a

A

¡Fig. 1.

The Blowpipe is generally made of brass. Fig. 1 represents the one described and used by GAHN, and ap

proved of by BERZELIUS.

Its points are turned and bored of three different sizes, and are partly of Platinum and partly of Brass. The first of platinum, contains the narrowest apertures, and is employed for qualitative analysis; the second, of brass, is used for such qualitative experiments as require a strong oxidation flame, and for heating silver, gold, and copper, in quantitative assayings, also for the roasting of copper, lead, and tin ores, the metallic contents of which are to be determined with precision; and the third, which is manufactured of the same material, contains the widest bore, and is for obtaining the quantitative proportions of lead and tin.

The platinum points, however, are always preferable to those of brass, because by a moderate red heat used on charcoal before the flame of the Blowpipe, they are more easily cleaned from the sooty particles obstructing their apertures. This method of cleansing cannot be applied to brass points, on account of their rapid oxidation; to prevent this, the operator must adapt to the opening a sharp-pointed fragment of horn, or a small needle, ground to one-half of its length; by this means, the aperture through which the air passes is purified. The black matter, adhering to the exterior of the tube, can be easily removed with a small wooden or leaden file, upon which is placed a quantity of fine moistened bone ash.

B

To defend the lips from injury, a mouthpiece of horn—C— is affixed to the Blowpipe. If, during the act of blowing strongly, this mouthpiece be pressed to the lips, partially open a much greater blast can be obtained than otherwise; and when

an operator once becomes accustomed to its management, his lips will not be fatigued. All who employ this instrument should have a suitable mouthpiece.

A Blowpipe entirely of silver is not to be recommended for quantitative researches, because at such experiments the manipulator must often blow uninterruptedly for several minutes, and the silver, being a good conductor of heat, becomes so hot that it cannot be held between the fingers, unless enclosed in a nonconducting substance.

Fig. 2.

When the Blowpipe was required for glass, BERZELIUS employed a tube bent to a right angle ;-see Fig. 2. This tube will be found convenient, as it can be turned in many directions, to suit the materials operated upon.

When the hands are required for examinations, the Blowpipe should have affixed a very broad mouthpiece of bone; as by this means it can be held safely.

II. THE COMBUSTIBLE MATERIAL.

In many qualitative examinations with the Blowpipe, an operator may employ the flame from wax, tallow, or an oil-lamp. These, however, offer very great inconveniences in consequence of the carbonaceous matters which they hold mechanically being deposited upon the substance under examination, thus depriving the operator of the opportunity of making any notes as to change of color or the like; besides, the heat they afford is never so high as to answer the requirements of the assayist; even the gas flame, which is the most convenient for Blowpipe operations, cannot be used naked, but after a sufficient volume of air is mixed with the gas, to oxidize its carbon, this mixture, on being ignited, answers every purpose, and is now generally resorted to in all laboratories.