of ammonia is sometimes used for the same purpose. A dilute solution of this salt is poured upon the filter, after the washing has been completed. The filter contains, consequently, after exsiccation, a small amount of this salt, which facilitates the incineration of the paper. In the fourth place, we must avoid conducting the process in crucibles made of materials likely to be effected by the precipitate. We have already had occasion, in the qualitative analysis, to point out those cases in which the use of platinum crucibles ought to be avoided. SECTION II. REAGENTS. 33. For general remarks upon reagents necessary to the student, I would refer him to my volume on qualitative analysis. We shall confine ourselves here to the preparation, tests, and most important uses of those chemical substances which subserve principally and more exclsively the purpose of quantitative analysis, simply enumerating the rest. The same classification which I adopted in my qualitative anasis, is retained here, not because it is free from objection, but because upon the whole I deem it the best. A. REAGENTS IN THE HUMID WAY. a. Reagents principally used as simple solvents. § 34. 1. DISTILLED WATER. Water intended for quantitative investigations must be perfectly Water distilled from glass retorts is not chemically pure, G but leaves a minute residue upon evaporation. This defect renders it inapplicable in many experiments; thus, for instance, we cannot use it to determine the exact degree of solubility of substances which are only slightly soluble. (Vide experiment No. 1.) In many cases it is necessary to free the water by ebullition, from atmospheric air and carbonic acid. 2. ALCOHOL. 1. Absolute alcohol. 2. Spirits of wine of various degrees of strength. 3. ETHER. The officinal ether of commerce is sufficiently pure. The application of ether as a solvent is very limited. It is more frequently mixed with spirits of wine, in order to diminish the solvent power of the latter for certain substances (e. g. chloride of platinum and ammonium). B. Reagents which are principally used as chemical solvents. $ 35. 1. HYDROCHLORIC ACID. An acid of 1.12 sp. gr. suffices for most purposes; in some cases, however, it is required to be stronger. 2. NITRIC ACID. An acid of 1.2 suffices for most purposes. 3. NITROSO-NITRIC ACID, (RED FUMING NITRIC ACID). Preparation. Two parts of pure and dry nitrate of potass are introduced into a retort, and one part of hydrated sulphuric acid is poured upon this salt, either through the tube of the retort, or if a common retort is used, through the neck of the latter by means of a long funnel tube bent at the lower extremity; this should be done carefully so as not to soil the neck of the retort. The latter is then placed in a sand-bath, and connected with a receiver, but not quite air-tight. The distillation is conducted at a gentle heat, and carried to dryness. The receiver must be constantly kept covered during the distillation. Tests.-Red fuming nitric acid intended for analytical purposes, must be in a state of the greatest possible concentration and perfectly free from any admixture of sulphuric acid. Uses. This acid is a powerful solvent and oxidising agent; it serves more especially to convert sulphur and the sulphurets into sulphuric acid and sulphates. 4. AQUA REGIA. 5. ACETIC ACID. 6. CHLORIDE OF AMMONIUM. Y. Reagents which serve principally to separate substances into general classes or groups. $ 36. 1. SULPHURIC ACID. a. CHEMICALLY PURE AND CONCENTRATED SULPHURIC ACID. Preparation. From three to four pounds of common sulphuric acid are introduced into a capacious glass retort, coated externally with a paste made with clay and cow-hair; a coil of platinum wire, or a few fragments of platinum, are thrown into the retort, and the latter is placed deep into a wind furnace, (which is subsequently to be covered with a cap ;) the neck of the retort is then introduced into the body of a large globular receiver, without luting. The contents of the retort are gradually heated to boiling, by surrounding the latter with red-hot charcoal, taking care in the course of the operation to make the fire act principally upon the top and sides, and less upon the bottom, of the receiver. If these instructions be strictly followed, the distillation will proceed quietly, and the operator need be under no apprehension of danger. The acid which passes over first is contaminated with nitric acid; it is necessary, therefore, to change the receiver after the lapse of some time, in order to obtain absolutely pure acid; the distillation is continued until about three quarters of the acid in the retort have passed over. The distillation may likewise be conducted in the sand-bath; in this case the bath should be so constructed that its bottom is covered with a considerable amount of sand, and that upon placing the retort into it, there remains but a small interval between the sides of the retort and the walls of the bath; the retort is covered with sand and a very inclined position given to the neck. The further operation is conducted exactly as the above. In this manner (i. e. in the sand-bath) ten pounds or more of sulphuric acid may be distilled at once without danger. Tests. If chemically pure, sulphuric acid will not leave the slightest residue when evaporated in a clean platinum dish. b. COMMON SULPHURIC ACID. C. DILUTE SULPHURIC ACID. Dilute sulphuric acid, is prepared by mixing one part of concentrated sulphuric acid-(chemically pure or common, according to the circumstances of the case)-with five parts of water. 2. SULPHURETTED HYDROGEN. a. Sulphuretted hydrogen gas. PLATE XXX. The cleaning of the the tube through which this gas is conveyed, when needed for analytical purposes, may be materially facilitated by giving to the tube the construction illustrated by Plate XXX. b. Sulphuretted hydrogen water. 3. HYDROSULPHURET OF AMMONIA. 4. SULPHURET OF POTASSIUM. 5. POTASS (pure potass ley.) 6. CARBONATE OF POTASS. 7. CARBONATE OF SODA. One part of the anhydrous salt is dissolved in about ten parts of water. As a neutralizing and precipitating agent, this is in many cases preferable to carbonate of potass. 8. AMMONIA. 9. CARBONATE OF AMMONIA. 10. CHLORIDE OF BARIUM. 11. NITRATE OF BARYTES. 12. CYANIDE OF POTASSIUM. This substance is extensively used in separate certain metals from one another. quantitative analysis to The aqueous solution of it must be prepared every time it is needed for use, since it does not keep, even in close vessels. 13. NITRATE OF SILVER. 14. CHLORINE. II. SPECIAL REAGENTS IN THE HUMID WAY. a. Reagents which serve principally to determine or to separate individual bases. $37. 1. PHOSPHATE OF SODA. 2. OXALATE OF AMMONIA. 3. SUCCINATE OF AMMONIA. Preparation.-Saturate succinic acid,-which has been purified by re-crystallization from its solution in nitric acid,-with dilute |