lose nitrates and water are formed; thus, CH10O5 + 2HNO, C¿H ̧(NO3)2O3+2H2O. The exact character of the reaction depends upon the strength of the acid used, the temperature at which the cotton is immersed, and the length of time maceration is continued; thus, di-, tri-, tetra-, penta-, and hexanitrate may be produced. The last two compounds are insoluble in alcohol and ether, and hence unfit for the purposes of official pyroxylin, which latter probably consists of a mixture of cellulose di- and trinitrate. It is important that the acids used be of official strength, and that the acid mixture, which becomes heated, be allowed to cool down to 32° C. (90° F.) before the cotton is added, otherwise, in the latter case, the higher nitrates are formed and the staple of the cotton is destroyed; if weak acids be employed, prolonged maceration becomes necessary and imperfect nitration may result; in either case the product is insoluble.

In order that the cotton may be completely saturated with the acid mixture, it should be introduced in small portions, by the aid of a glass rod. The sulphuric acid used takes no part in the reaction, but facilitates the same by removing the water which is eliminated.

Pyroxylin was at one time looked upon as a nitro substitution compound, and called nitrocellulose, the group NO, having been supposed to replace hydrogen in cellulose. Further studies of cellulose and the behavior of pyroxylin toward reagents have shown the latter compound to be a nitric acid ester or compound ether, formed by the displacement of hydrogen in the hydroxyl groups by the nitric acid radical, as shown by the formulas, C.H.(ONO2)2O, or C,H,(ONO),0,. The correctness of this view is shown by the fact that nitric acid can be abstracted from cellulose nitrates by treatment with alkalies, and can also be completely displaced by concentrated sulphuric acid, even in the cold. All cellulose nitrates can be converted back into cellulose by reducing agents, and the degree of nitration can be definitely determined by treatment with ferrous sulphate and hydrochloric acid, the nitric oxide liberated being collected in a graduated tube, and from this the amount of nitric acid present can be calculated ; the following equation explains the reaction: 2C¿H,(ONO2),O2 + 18HCl +18 FeSO4 = 2C¿H1005 + 6NO + 6Fe2(SO1); + 3FeCl¿ + 6H,O.

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Pyroxylin is used in pharmacy exclusively in the preparation of plain and medicated collodion (see page 284), but has met with more extensive application in the arts in the manufacture of celluloid, a mixture of pyroxylin and camphor.

THE PRODUCTS OF DISTILLATION. When wood is subjected to heat in air-tight cylinders or retorts a number of new substances are obtained, as a result of destructive distillation, the character of which depends largely upon the degree of heat employed and the care with which the process has been conducted. Both liquid and gaseous products are formed and distil over, while the solid residue is either charcoal or the original wood employed, but slightly altered in

appearance. The liquid distillates include an acid fluid and tar; the former is known as pyroligneous acid or wood vinegar, which contains, besides acetic acid, acetone, C,H,O, methyl or wood alcohol, CH,OH, furfurol, C,H,O2, catechol or pyrocatechin, C ̧H(OH)2, and other substances.

ACETIC ACID. Although this acid can be produced by the oxidation of weak alcoholic liquids, it is obtained for the trade by distillation of wood. In order to avoid, as far as possible, contamination with empyreumatic products, the distillation is carried on at a temperature below that at which the formation of charcoal occurs, or below 220° C. (428° F.). At the extensive acetic acid works of E. R. Squibb & Sons, in Brooklyn, N. Y., oak wood cut into small pieces, about four inches in length, is fed into large rectangular iron retorts, which are then heated in appropriate furnaces and kept at a temperature of 205° C. (401° F.) for a period of seven days, during which time a slightly colored liquid, dilute crude acetic acid, distils over, the wood losing about one-half in weight and assuming a dark walnut color and slight empyreumatic odor, but retaining its original structure and elementary composition. The acid liquid is neutralized with soda ash or sodium carbonate, and the resulting sodium acetate, having been obtained dry by evaporation, is roasted on top of the furnaces heating the retorts, whereby empyreumatic products are destroyed and water and other volatile matter driven off. Upon treating the sodium acetate with sulphuric acid, in suitable stills, purified acetic acid is recovered.

If wood is distilled at temperatures above 230° C. (446° F.), the resulting wood vinegar is more or less highly colored and possesses a strong empyreumatic odor. It requires a more tedious process of purification by means of milk of lime, whereby soluble calcium acetate is formed and many impurities are precipitated as insoluble calcium compounds; the calcium acetate can be converted into sodium acetate by treatment with sodium sulphate, which is then further purified by solution, recrystallization, roasting, etc., and is finally decomposed by distillation with sulphuric acid.

Chemically, acetic acid may be looked upon as methane or marshgas (CH), in which an atom of hydrogen has been replaced by the carboxyl group, CO,H, forming a monobasic acid, thus: CH,CO,H= HCHO. It is a remarkably stable acid, and, although rich in oxygen, is not decomposed at moderately high temperatures, nor is it readily affected by oxidizing or reducing agents.

The Pharmacopoeia recognizes three grades of acetic acid, which are officially designated as glacial acetic acid, acetic acid, and diluted acetic acid, and contain, respectively, 99, 36, and 6 per cent. of absolute HC,H,O2. The three acids, recognized by the same names in the British Pharmacopoeia, correspond very closely in strength to the above, containing 99, 33, and 4.27 per cent. of absolute acetic acid respectively; but in the German Pharmacopoeia the term

acetic acid is used to designate a solution containing 96 per cent. of absolute acid, while the German diluted acetic acid contains 30 per cent.

Specific gravity is of no value in the examination of acetic acid, since the maximum density is reached in an 80 per cent. solution; beyond this point the specific gravity again decreases until absolute acetic acid is reached, having a density of 1.053. Official glacial acetic acid and an acid of 46 per cent. have the same specific gravity, 1.058, at 15° C. (59° F.), and, if diluted with water, the density of the weaker acid only will fall, that of the stronger acid increasing; between 73 and 84 per cent. acetic acid the specific gravity is almost stationary, the rise between these two points amounting to not more than 8 ten thousandths. Titration with normal alkali solution, as directed in the Pharmacopoeia, is the only correct means of ascertaining the strength of acetic acid solutions, each Cc. of KOH solution corresponding to 0.05986 Gm. of absolute HC,H2O2, as shown by the equation, KOH+HC2H2O2=KC2H2O2+H2O.

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Glacial acetic acid is obtained by distilling anhydrous sodium. acetate with highly concentrated sulphuric acid and exposing the resulting liquid to a temperature below 10° C. (50° F.); after crystallization has taken place, the remaining liquid may be drained off and again exposed to cold to secure a further yield of crystals. Glacial acetic acid of official strength should retain its crystalline form at least until a temperature of 15° C. (59° F.) is reached, when it slowly begins to liquefy; much of the so-called glacial acetic acid of commerce is simply a strong solution, containing from 75 to 85 per cent. of absolute acid and does not solidify at a temperature of 5° C. (41° F.) or even lower.

The Pharmacopoeia directs the use of glacial acetic acid in the preparation of solution of ferric acetate, and it is also employed as an excellent solvent for certain essential oils, resins, and fatty bodies. The acid absorbs moisture from the air, and must therefore be preserved in tightly-stoppered bottles.

Official acetic acid is obtained, like the glacial acid, by distilling sodium acetate with sulphuric acid and finally adjusting the strength to the requirements of the Pharmacopoeia. It should contain 36 per cent. of absolute acetic acid, and is used in pharmacy chiefly for the preparation of the official diluted acid, and also as an addition to the menstruum employed for tincture of sanguinaria and several fluid and solid extracts.

Acetic acid for pharmaceutical purposes should be free from empyreuma, which may be detected by means of potassium permanganate, the color of which is readily discharged by empyreumatic substances. Upon neutralizing the acid with alkali and warming no foreign odor should be perceptible.

Pharmacists will find it to their interest to purchase strong acetic acid and dilute this to suit their requirements, according to the rule given on page 65. Acetic acid of 60 and 80 per cent. strength can

be purchased from reliable manufacturers at relatively lower prices than the official acid.

During the past few years many experiments have been made with the view of utilizing a strong (60 per cent.) acetic acid in place of 'alcohol for the extraction of aromatic, alkaloidal, and resinous principles from vegetable drugs. The results thus far obtained have been very encouraging, and manufacturers have already successfully applied this new menstruum in the preparation of certain aromatic solutions.

As the Pharmacopoeia requires the official acetic acid to contain 36 per cent. of absolute HC,H,O2, each gramme of the acid will neutralize exactly 6 Cc. of normal potassium hydroxide solution. The commercial variety of acetic acid known as "No. FIG. 280. 8" should never be used in place of the official acid, as it is weaker, containing only 30 per cent. of absolute acid.

Diluted acetic acid, recommended in the Pharmacopoeia in place of commercial vinegar as a menstruum for several official preparations, is made by mixing 100 Gm. of the 36 per cent. acid with 500 Gm. of water, and contains, therefore, 6 per cent. of absolute HC,H,O2. Its advantages over ordinary vinegar are purity and uniformity of strength, besides which the entire absence of color enables it to be used for colorless solutions, such as spirit of Mindererus and the like.

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While titration with normal alkali solution is always to be preferred as a means of ascertaining the strength of dilute solutions of acetic acid, other methods are also employed, such as neutralization with sodium or potassium bicarbonate, or with a standard ammonia solution, in an instrument known as Otto's acetometer, see Fig. 280. The latter method is largely used in vinegar establishments and gives results accurate to within one-fifth of one per cent. The acetometer consists of a graduated glass cylinder with rounded bottom, 36 centimeters (14.4 inches) in length and 3 centimeters (0.8 inch) internal diameter. The lower two graduations, marked a and b, indicate a volume of 1 and 10 Cc. respectively, while the upper part, from 6 to 12, is divided into 48 spaces each equivalent to 0.52 Cc., hence the large space between any two figures represents 2.08 Cc. The solution of ammonia used for the test contains 1.4 per cent. of absolute NH, and is prepared by mixing 14 Gm. of official 10 per cent. ammonia water with 86 Gm. of distilled water; every 2.07 Gm. of the solution measure 2.08 Cc. and correspond to 0.1 Gm. of absolute HC,H,O,. When vinegar is to be tested, 1 Cc. of litmus test-solution is first poured into the tube, 10 Cc. of vinegar are then added, whereby the color of the litmus solution is changed to red, and finally sufficient of the above mentioned ammonia solution until, with gentle agitation, the blue color of the liquid is

Otto's

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restored. From the volume of ammonia solution used, as shown by the graduated cylinder, the amount of absolute acetic acid present can be readily calculated.

When chlorine is allowed to act on acetic acid in the sunlight, chloracetic acid is formed, three varieties of which are known, the most important being trichloracetic acid, HC2ClO2. This latter compound occurs in deliquescent crystals, and is obtained by treating chloral hydrate with fuming nitric acid, exposing the mixture to sunlight for several days until red fumes are no longer evolved and then distilling.

Among the substances associated with acetic acid in crude wood vinegar are two of greater interest to pharmacists than the rest-acetone and methyl alcohol. Acetone, CHO or CH,COCH,, also known as pyroacetic spirit, was heretofore obtained on a commercial scale solely by the destructive distillation of acetates (chiefly calcium acetate), but recently (1895) a process has been devised by Dr. E. R. Squibb for decomposing acetic acid vapor at a high temperature, between 500° and 600° C. (932° and 1112° F.), in a specially constructed iron rotary apparatus, whereby a large yield of fairly pure acetone may be secured. The crude acetone thus obtained is afterward purified by dehydration with caustic lime and redistillation. The decomposition of acetic acid vapor results in the formation of acetone and carbon dioxide with the liberation of water, thus: 2HC2H2O, =С2H2O+CO2+H2O. The process and apparatus are fully described in Ephemeris, vol. iv., No. 3.

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Chemically, acetone belongs to the class of compounds known as ketones, which consist of two alcohol radicals united by means of the bivalent group CO, called carbonyl; hence acetone is also called dimethyl ketone, and may be looked upon as acetic aldehyde, CH,COH, in which the hydrogen atom is replaced by the methyl

group.

Acetone is now extensively employed for the manufacture of chloroform, and has been found a valuable solvent for oleoresins, collodion cotton, etc. When pure it is a colorless, mobile, inflammable liquid of 0.7966 specific gravity at 15° C. (59° F.), and boiling at 56.3° C. (133.34° F.). It is miscible in all proportions with water and alcohol, hence the commercial article is usually contaminated with these substances.

Methyl alcohol, or wood alcohol, CH,OH, also known as pyroxylic spirit, or wood naphtha, boiling at a comparatively low temperature-66° C. (150.8° F.)-may be obtained in a crude state by distilling wood vinegar after neutralizing with sodium carbonate or lime, and collecting the first portions coming over; wood vinegar usually contains about 10 per cent. of wood alcohol. It is purified by heating in a water-bath, with an excess of anhydrous calcium chloride, with which methyl alcohol forms a crystalline compound, CaCl2 + 4CH,OH, and, after all volatile matter has been dissipated, mixing the crystals with water and distilling, whereby the compound