This apparatus is not provided, like the other, with a pressure gage, from the fact that the pressure being the result of a mechanical cause, the operator will soon be able to judge the amount of pressure by the number of strokes of the piston. The delivery pipe is similar in every respect to the one in the apparatus described formerly; the graduated tube outside showing the quantity of liquid inside the apparatus is also the same; in fact, the similarity between the two is striking. But the principal feature of the apparatus, and that which recommends it to the profession, is the perfect isolation of all the working parts of the apparatus from direct contact with the liquid injected. The greatest objection in this case, as in the other, is removed, as the most important part of the work, namely: that of compressing the air, is performed without any danger to the generator. Another apparatus—that of Waldon—combines the two systems in one, and can be operated with equal facility either by means of compressed air or by means of gaseous expansion. Still, these instruments require a certain amount of familiarity in the handling before they can be operated with efficiency, as, to a person not fully conversant with their mechanism, they may prove awkward. The instruments of Messrs. G. Tiemann & Co., of New York, which I have employed so far very successfully, could be rendered perfect by adopting some modifications in their make. GASEOUS COMPOUNDS. Too little attention has been paid heretofore to the antiseptic powers of certain gases. It is a well known fact, that some of the gases which are the result of animal and vegetable decomposition are, to a certain extent, the means of their own disinfection; hence, some of these are endowed with deodorizing as well as antiseptic properties. We have already given at length the properties of chlorine. Carbonic acid gas is another of those antiseptic agents which will occupy our attention. It exists in the atmosphere as a product of combustion and of the respiration of animals; it is a result, also, of the slow decomposition of most vegetable substances, and is evolved in great quantities from the ground in volcanic countries. In the formation of sugar it is produced in abundance, along with alcohol. For the purposes of the chemist, it is generally prepared by decomposing marble by means of some stronger acid. From its cheapness and the solubility of the residual salt, muriatic acid is generally employed.