test a portion for cobalt on a borax bead in the blowpipe-flame (=blue colour); dissolve the remainder in a few drops of hydrochloric with one or two of nitric acid, and if cobalt is not present, test at once for nickel by solution of potash or soda (=green precipitate); if cobalt is present, evaporate the acid solution nearly to dryness, add acetic acid and then nitrite of potassium, set aside; and when the yellow cobalt precipitate has separated, filter, and then add potash or soda for nickel. The carbonate-of-ammonium precipitate may not contain the whole of the barium, strontium, and calcium in the mixture unless free ammonia is present; for the carbonates of those metals are soluble in water charged with carbonic acid. If, therefore, the liquid is not distinctly ammoniacal, solution of ammonia should be added.- -Neither carbonate nor hydrate of ammonium wholly precipitate magnesian salts; and as a partial precipitation is undesirable, a solvent, in the form of an alkaline salt (chloride of ammonium), if not already present, must be added. The search for lithium may usually be omitted. Should a precipitate, supposed to be due to lithium, be obtained, it must be tested in a flame (=scarlet tint), as a little magnesium not unfrequently shows itself under similar circumstances. If present only in minute proportions, the lithium may also remain with the alkalies; it can then only be detected by physical ana– lysis (by a prism) of the light emitted from a tinged flame; by, in short, an instrument termed a spectroscope. Such a method of examination is termed spectrum analysis, a subject of much interest and of no great difficulty, but scarcely within the range of Pharmaceutical Chemistry. ACIDS. The radicals which have up to this point mainly occupied the attention of the student are (admitting ammonium) metals; and they have been almost exclusively studied not in the free state, but in the condition in which they exist in salts. Moreover these metals have been treated as if they formed the more important constituent, the stronger half, the foundation or base, of salts. Attention has been continuously directed to the metallic or basylous side of salts. There is still one more basylous radical worthy of a passing notice, though it usually plays only a subordinate part in reactions; and this radical, differing from the others that have been studied, is, so far as we know at present, a non-metal-Hydrogen. Unlike the salts of the metals, too, the salts of hydrogen are never, in medicine or the arts generally, used for the sake of their hydrogen, but always for the other half of the salt, the acidulous side. And it is not for their basylous radical that these hydrogen salts are now commended to the notice of the student*, but in order that he may study, under the most favourable circumstances, those acidulous groupings which he has been continually meeting in operations on salts, but which, to him, were for the time of secondary importance. He may now treat them as the primary objects of attention; and there is no better way of doing so than in operating on their compounds with hydrogen, the relatively inferior importance of which element, as compared with potassium, iron, &c., will * It must not be forgotten that the commonest salt of any radical whatsoever is a salt of hydrogen, the oxide of hydrogen (H2O), water. In the reactions already performed, the value of this compound has been constantly recognized, both for its hydrogen and for its oxygen, but most of all as the vehicle or medium by which nearly all other atoms are enabled to come into that contact with each other without which their existence would be almost useless; for some atoms are like some animals, out of water they are as inactive as fishes. It is true that both fishes and salts have usually to be removed from water to be utilized by man; but before they can be assimilated, either as food or as medicine, they must again seek the agency of water. serve to give the desired prominence to the acidulous bodies in question. These salts of hydrogen are the common, sharp, sour bodies termed acids (from the Latin root acies, an edge). The following Table includes the formulæ and names of the most important. A few of those mentioned are unstable or somewhat rare; in such cases a common metallic salt containing the acidulous radical may be used for reactions in the place of the hydrogen salt: -- HC,H,O, 2 3 2 H,S 4 3 H.CO 2 HCHO 2 4 4 6 HCHO chloric acid. boracic acid. acetic acid *. hydrosulphuric acid †. tartaric acid. phosphoric acid. The student will at once notice a prominent point of difference between the basylous radicals he has met with up to the present time and the acidulous groupings now brought before him. The former are nearly all elements, ammonium only being a compound; the latter are mostly compounds, chlorine, bromine, iodine, and sulphur being the only elements. This difference will not, how *The hydrogen on the acidulous side must not be confounded with the basylous hydrogen in all these hydrogen salts or acids; the two perform entirely different functions. Hydrogen in the acidulous portion is like the hydrogen in the basylous radical ammonium, it has combined with other atoms, to form a group which plays more or less the part of an elementary radical, and to which a single symbol is not unfrequently applied (Am; Cy, A, O, T, C, &c.). Cobalt, chromium, iron, platinum, &c. resemble hydrogen in this respect in often uniting with other atoms to form definite acidulous radicals in which the usual basylous character of the metals has for the time disappeared. † Synonyms:-sulphydric acid and sulphuretted hydrogen. ever, be so apparent when the chemistry of alcohols, ethers, and such bodies has been mastered, for they are all salts of compound basylous radicals. The above acids contain the only acidulous groupings that commonly present themselves in analysis, or in pharmaceutical operations. There are, however, several other acids (such as hypochloric, nitrous, hypophosphorous, valerianic, benzoic, gallic, tannic, uric, hyposulphurous, hydroferrocyanic, hydroferrideyanic, &c.) with which the student should be more or less familiar; reactions concerning these will therefore be described. Arsenious, arsenic, stannic, manganic, and chromic acids have already been treated of in connexion with the metals they contain; in practical analysis they always become sufficiently altered to come out among the metals. A glance at the foregoing Table is sufficient to show the quantivalence of the acidulous radicals, if so they may be called. The first eight are clearly univalent; then follow six bivalent, leaving two trivalent. These all combine with equivalent amounts of basylous radicals to form various salts; hence they may be termed monobasylous, dibasylous, and tribasylous radicals. The acids themselves are often spoken of as monobasic, dibasic, and tribasic respectively, or monobasic and polybasic. The practical study of the acidulous side of salts will occupy far less time than the basylous. Salts will then be briefly examined as a whole. One word of caution. It is only for purposes of convenience in the division of chemistry for systematic study that salts may be considered to contain basylous and acidulous radicals, or separate sides, so to speak; for we possess no absolute knowledge of the internal arrangement of the atoms (admitting that there are such things) in the molecule of a salt. A salt is probably a whole, having no such sides as those mentioned. HYDROCHLORIC ACID. Formula HCl. Molecular weight* 36.5. The acidulous radical of hydrochloric acid and of other chlorides is the element chlorine (Cl). It occurs in nature chiefly as chloride of sodium (NaCl), either solid, under the name of rock-salt, * The weight of a molecule is the sum of the weights of its atoms. mines of which are not unfrequently met with, or in solution in the water of all seas. Common table-salt is more or less pure chloride of sodium in minute crystals. Chlorine, like hydrogen, is univalent (Cl'); its atomic weight is 35-5. For the method by which it is prepared, and its properties, see page 12. REACTIONS. First Synthetical Reaction.-To two or three fragments of chloride of sodium add a few drops of strong sulphuric acid; colourless and invisible gaseous hydrochloric acid is evolved, sulphate of sodium remaining. Adapt to the mouth of the testtube, by a perforated cork, a piece of glass tubing bent twice at right angles, and convey the gas into another test-tube containing a few drops of water; solution of hydrochloric acid results. The product of this operation is the liquid commonly termed hydrochloric acid. When of certain given strengths it forms Acidum Hydrochloricum, B. P., and Acidum Hydrochloricum Dilutum, B. P. The process is also that of the Pharmacopoeia, larger vessels being employed, and the gas being freed from any trace of sulphuric acid by washing. Other chlorides yield hydrochloric acid when heated with sulphuric acid; but chloride of sodium is always used because cheap and common. The acid is a by-product in the manufacture of carbonate of sodium (p. 205). Invisible gaseous hydrochloric acid forms visible greyish-white fumes on coming into contact with air. This is due to combination with the moisture of the air. The intense greediness of hydrochloric gas and water for each other is strikingly demonstrated on opening a test-tube full of the gas under.water; the latter rushes into and instantly fills the tube. If the water is tinged with blue litmus, the acid character of the gas is prettily shown at the same time. The test-tube, which should be perfectly dry, may be filled from the delivery-tube direct, for the gas is somewhat heavier than, and therefore readily displaces, air. The mouth may be closed by the thumb of the operator. The process, as described in the British Pharmacopoeia, includes the use of more sulphuric acid than is theoretically necessary; |