[239]. Medical Transactions, vol. vi, p. 414.
[240]. See Appendix, page 277.
[241]. This substance may be said to consist of Charcoal, in a state of extremely minute division, and the sub-carbonate of Potass. It is prepared by deflagrating, in a crucible, two parts of Super-tartrate of Potass with one part of Nitrate of Potass.
[242]. In order to close the end of the tube, where a blow-pipe is not to be procured, (which, says Dr. Bostock, we may suppose upon these occasions will often be the case) the end is to be placed in a common fire until it is completely softened, and a pair of small tongs being at the same time made red hot, the tube is to be withdrawn from the fire, and the heated end pinched by the tongs, and at the same time bent up at an acute angle, so as to be brought parallel to the body of the tube. The tube is then to be heated a second time, and being again firmly pinched by the hot tongs, the end will be found to be completely impervious.
[243]. Dr. Bostock states that the best proportions for this coating are, one part of common pipe clay, to three parts of fine sand; which are to be well kneeded together, and reduced to such a state of tenacity, that the lute will readily adhere to the tube, and its different parts unite without forming a visible seam. “Observations on the different methods recommended for detecting minute portions of Arsenic, by J. Bostock, M.D.” Read before the Liverpool Medical Society, and published in the Edinburgh Med. and Surg. Journ. April, 1809.
[244]. See the paper above quoted.
[245]. Black’s Lectures, v. ii, p. 430.
[246]. Foderé recommends this process, Traité de Med. Leg. t. iv, p. 153; and Dr. Jaeger, in his Thesis, before quoted, observes that he has been enabled to recognise the tenth of a grain of arsenious acid, although mixed with sugar, by its odour, when thrown upon burning coals! We must be allowed to question this fact; Dr. Jaeger, no doubt, believed that he recognised the alliaceous odour, but it must have been the sole effect of the imagination. Dr. Bostock states that such a test is not to be depended upon; for, unless the arsenic be in considerable quantity, the odour is not sufficiently perceptible; and if it be mixed with either an animal or a vegetable substance, the smoke and smell arising from these bodies, when heated, will altogether prevent our recognising the peculiar odour of the arsenic. When a quantity of arsenic is mixed with an equal weight of flour, and placed upon iron at a low red heat, so as not to cause the flour to inflame, the suffocating smoke that arises from the latter can be alone perceived; nor is it possible to discover that any thing has been mixed with it. Edinb. Med. Journ. l. c. This last objection of Dr. Bostock is true in fact, although it admits of a different explanation, for at a low temperature the arsenious acid will be volatilized without decomposition; in which case no alliaceous odour can be developed.
[247]. The paper was read before the Liverpool Medical Society.
[248]. London Dispensatory. Edit. 3, p. 176.