Specific Gravity. TABLE showing the PERCENTAGES OF HYDRATED ACID corresponding to various TABLE showing the Percentages of Anhydrous Acid corresponding to various specific gravities of Aqueous Hydrochloric Acid, by URE. Temperature 15° C. TABLE showing the Percentages of Hydrated and Anhydrous Acids corresponding to various specific gravities of Aqueous Sulphuric Acid, by BINEAU; calculated for 15° C., by OTTO. 34.24 30-76 25.00 22.27 14.28 5 00 1-63 The more generally useful method is, how ever, to prepare an alkaline fluid of known strength, and neutralise the acid. In order to do this, the operator requires burettes, tincture of litmus, or litmus paper, a dilute acid of known strength, and a dilute alkaline fluid also of known strength. The acid solution must in all cases be diluted so as to contain an exact equivalent number in grammes or grains of the acid in 1000 c. c. or parts. For instance, 40 grammes of sulphuric, 36:46 of hydrochloric, 63 of oxalic to the litre. These solutions are called normal acids. The normal alkaline solution is made so that one volume of it exactly neutralises one volume of the acid solution. Soda is nearly always used. In order to prepare it, a solution of soda is made, and diluted until about the specific gravity 105, which corresponds to 3:6 per cent. of soda. A portion of it is then run from a burette, until it exactly neutralises 30 c. c. of a normal acid solution. The exact point of neutrality is determined by litmus. Suppose 27 c. c. of soda neutralises 30 of the acid, then it is too strong; to every 27 c. c. 3 c. c. of water must be added-i.e., 111'1 to the litre. The solutions of normal acid must be prepared with great care; the acids used must be absolutely pure. A solution of oxalic acid Fresenius does not think so good for acidimetry as hydrochloric acid, on account of the difficulties in drying the former. (See ACID, OXALIC.) The normal hydrochloric acid is thus prepared :-900 c. c. of water are mixed with 180 c. c. of ordinary pure hydrochloric acid of 1.12 specific gravity. Fill a burette with the mixture, measure off two quantities of 20 c. c. each, precipitate the acid with nitrate of silver, carefully filter, dry, ignite, and weigh the resulting precipitate: the two precipitates should agree very closely. Take the mean of them, and calculate from them how much E.g., suppose 20 c. c. contained 810 grammes of hydrochloric acid, therefore 1000 c. c. contains 40.5 grammes, consequently we have water must be added to 1000 c. c. 36.46 : 1000 :: 40.5 : x -11108 Hence 1110.8 must be added to the litre of water. Normal sulphuric acid is prepared on a similar plan, only it is precipitated by chloride of barium. (The resulting sulphate, if multiplied by 34335, gives the sulphuric acid.) The actual analysis is performed by taking a determinate quantity, say 100 c. c., of the liquid to be examined, and dropping from a burette the alkaline liquid until exact neutrality, as determined by litmus paper or tincture of litmus, and the number of centimetres used will indicate the amount of free acid. The following table will be found useful: WEIGHT of the RESPECTIVE ACIDS equivalent to the given weight of the principal bases, distilled water, in such proportions as will leave a large amount of the acid undissolved, and shaken. Filter, crystallise, and let the crystals drain dry at the ordinary temperature in blotting-paper. Another process is to decompose oxalate of lead by dilute sulphuric acid. If the acid is prepared in this way, it has the formula H,C,O,2H2O, and its equivalent is accordingly 63. It is used by the analyst in various methods of analyses, especially in alkalimetry, acidimetry, and in standardising various volumetric solutions. Acid, Lactic (H,C6H1006) - A trans- | put into a flask, and treated with lukewarm parent, inodorous, syrupy liquid with a sharp taste; sp. gr. 2.215. It was first obtained by Scheele from whey. It is an important constituent of the gastric juice. It is found in muscular tissue, in small quantities in the urine and sweat, and has, in cases of diabetes, been met with in the saliva. It also exists in some plants, e.g., Nux vomica. When milk is said to turn sour, this sourness is due to a special fermentation. The caseine acts like diastase or other ferments. Peculiar cells, like those of yeast, but smaller, make their appearance, and lactic acid appears in the liquid; but as caseine is coagulated by acid, directly this change has taken place, the ferment caseine is coagulated, and the action stops, to be again renewed, however, if chalk, &c., is added to neutralise the acid. Besides milk, many other organic liquids will undergo this fermentation. It is, indeed, a frequent result of the acetification of vegetable substances. The most effective way of preparing the acid is that of Wackenroder. Digest together 25 parts of sugar of lead, 20 of powdered chalk, 100 of skimmed milk, 200 of water, at 75° F. In six weeks the chalk will be dissolved. The whole is then heated, but not to boiling; the cheese is separated, pressed, and the liquid decanted, clarified by albumen, and evaporated; the lactate of calcium crystallises. It may then be decomposed by sulphuric or oxalic acids. Acid, Meconic (μńкwv, a poppy)-This acid is contained in opium. Its formula is H3CHO7,3H2O. It strikes a blood-red colour with chloride of iron, and this fact forms the basis for a valuable test in suspected cases of opium poisoning. See OPIUM. Acid, Oxalic (Dihydric Oxalate) (H2CO 2H2O=90+36) — This substance is made on a very large scale by heating a mixture of hydrate of potash and sawdust. It may also be obtained by heating | tartaric, citric, or malic acid with potassic hydrate, and by boiling starch or sugar with nitric acid. The process above mentioned of obtaining oxalic acid from sawdust (Robert Dale & Co.'s patent) has so cheapened this acid, that whereas in 1851 it cost 16d. a pound, it now costs about half that. It occurs naturally in the wood-sorrel (Oxalis acetosella), in the Rumex acetosa, and in the leaf-stalks of the common rhubarb. It is of importance to obtain this acid perfectly pure. The purification of the oxalic acid of commerce is very easy. The process is carried out as follows :-The impure acid is In order to detect the acid in the contents of the stomach (which in such a case would be strongly acid), the contents are boiled with distilled water, filtered, then treated with a solution of acetate of lead. If oxalic acid is present, it will be precipitated as an oxalate of lead. This precipitate must be well washed, and then suspended in water, through which pass a stream of sulphuretted hydrogen, filter off the black sulphide of lead, evaporate to dryness, weigh and test the residue. Another way is by treating the oxalate of lead by sulphide of ammonium, and obtaining thus the oxalate of ammonia. Having obtained by either method a substance supposed to be oxalic acid or oxalate of ammonia, the following tests may be applied. Lime water gives a precipitate in solutions of oxalic acid of oxalate of lime, a white powder, insoluble in acetic acid, but soluble in strong mineral acids. If a little solid oxalic acid is treated with strong sulphuric acid in a test tube, it is decomposed, froths up, emitting carbonic acid and carbonic oxide, the latter burning with a blue flame. A solution of oxalic acid reduces the salts of gold. The former tests agreeing, with its physical properties, will easily identify the acid if present. Acid, Phenic-See ACID, CARBOLIC. Acid, Prussic (syn. Acid Hydrocyanic) — (HCy = 27) — Observed specific gravity of vapour 0·9476, of liquid 0·7058 at 446° (7° C.); melting-point, 5° F. (−15° C.); boiling-point, 80° F. (26·5° C.); rel. weight 13.5. This substance is a most deadly poison. In its concentrated state, it kills with a lightninglike rapidity; but in the dilute commercial form, even after a large dose, a few simple acts, such as walking to a bedroom door, putting a cork in a bottle, getting into bed, &c., have been performed. The symptoms are paleness, syncope, gasping for breath, convulsions, contracted pupils, nausea, insensibility, and death. The most appropriate remedy is ammonia, both internally and applied to the nostrils. A little weak liquor ammonia may, if time permit, be injected under the skin or into the veins. Chlorine water has also done good, and cold douches to the head. To detect the acid in the contents of the stomach, or in any fluid, if the smell, either of bitter almonds or of the acid itself, be perceptible, and the liquid have an acid reaction, simple distillation into a receiver, containing a little distilled water, will separate it in a tolerably pure state. If the reaction is alkaline, the liquid may contain cyanide of potassium-a very common salt. In such a case, a little sulphuric acid added to it, and then distilled as before, will separate it in the form of dilute hydrocyanic acid. The dilute prussic acid obtained by either of the above processes may be tested as follows:-Add a little liquor potassa, a few drops of a solution of sulphate of iron, and then a little perchloride of iron: the result is Prussian blue-the blue turned to brown by alkalies. This is very reliable evidence of prussic acid. Add nitrate of silver, a white precipitate, curdy, insoluble in cold dilute nitric acid, soluble in ammonia and cyanide of potash, denotes cyanide of silver, and is also a very reliable test. A very accurate and convenient method is to take two accurately-fitting watch-glasses, moisten the one with a little sulphuric acid, add a few drops of the liquid for examination, invert the other one over it, which must contain a little sulphide of ammonium. (Or the two watch-glasses may be placed the one above the other, in the ordinary way, under a glass shade.) After a little time the upper one is removed, dried, and perchloride of iron is added. If prussic acid is present, a blood-red colour is produced, which is discharged by bichloride of mercury, thus distinguishing it from the similar colour afforded by meconic acid. The chief forms in which prussic acid is ordinarily met with are 1. The dilute medicinal acid=2 per cent. anhy drous acid. 2. Scheele's acid = 2 per cent, anhydrous acid. 3. Cyanide of potassium, 2 grains 50 drops of medicinal acid. 4. Oil of bitter almonds 13 per cent. anhydrous acid. Acid, Pyroligneous - Impure acetic acid, obtained from the destructive distillation of wood. Owing to its impurities, which are of a tarry nature, it is a little more antiseptic than pure acetic acid. See ACID, ACETIC. Acid, Pyrogallic (C&H6O3)—This substance has no acid reaction. It forms bril liant plates, freely soluble in water, alcohol, and ether. It is prepared by subliming gallic acid, which may be mixed with pumicestone, and put in a retort, through which carbonic acid gas is passed. It is used in photography, and in the analysis of air and other gases, where it is of great value, from the fact that an alkaline solution of pyrogallic acid absorbs oxygen rapidly, and will completely remove it from air or other mixture of gases. Acid, Sulphurous (Sulphurous Anhydride)-Properly speaking, the latter is the proper name, as its chemical composition is represented by the symbols SO2; and it is composed of 1 volume of sulphur united with 2 of oxygen, the three volumes, at the time of combination, being condensed into two. The theoretic specific gravity of the gas is 2-2112; observed specific gravity, 2·247; of the liquid, 138 at 60°(15° C.); melting-point, -105° F. (-76°C.); boiling-point, 14° F. (10° C.) This substance is ordinarily in the form of a gas, but may be liquefied by intense cold. It is prepared for commercial purposes by deoxidising charcoal or sawdust by sulphuric acid, and distilling. It is accompanied in this case by half its volume of carbonic anhydride. In a pure state for the laboratory, 90 grammes of concentrated sulphuric acid are boiled with 15 grammes of copper clippings; the result is sulphate of copper, water, and pure sulphurous anhydride. It is also prepared by heating sulphur and oxide of manganese; and whenever sulphur is burned in air, this gas is formed. Properties and Uses.-The gas has a pungent, suffocating odour, and if a person inhales it slightly or entirely undiluted, it In a dilute form it rapidly causes death. acts simply as an irritant, and causes running at the eyes and nose, sneezing, &c. It quickly extinguishes flame, and is not inflammable. By passing it through a tube, cooled by a freezing mixture, it may be condensed to a bitumen. Water takes up 68 8 of its bulk of colourless transparent liquid, which dissolves this gas at 32° F., 435 at 59° F. (15° C.), and 32 at 75° F. (24° C.) Thus it is extremely soluble. When passed into water it combines with it, and is then converted into the real acid-sulphurous acid (HSO3)-but this compound has never been isolated. Sulphurous acid combines with bases, forming sulphites, bisulphites, and hyposulphites. This gas is extensively used by the bleachers of straw, wool, silken goods, isinglass, sponge, and other goods. It is a most excellent antiseptic. It is used in this country to keep casks sweet before putting cider, &c., in |