BACTERIOLOGICAL, PHYSIOLOGICAL, ETC. 89 ORGANIC ANALYSIS. Identification of Acids. E. E. Reid. ( J . Amer. Chem. Soc., 1917, 39, 124- 136.)-A new series of crystalline derivatives available for the identification of organic acids is readily prepared by the action of p-nitrobenzyl bromide on the potassium or sodium salts of the acids. The p-nitrobenzyl esters so formed usually crystallise well from dilute alcohol, and a large number of them are solids of well- defined melting-points.The reagent, p-nitrobenzyl bromide, is best prepared by heating p-nitrotoluene fotr some hours in a sealed tube at 125" to 130" C. with half the calculated quantity of bromine; the tube is opened and the hydrobromic acid allowed to escape, the other half of the bromine is then added, and the tube re- sealed and again heated.The product is dissolved in hot alcohol and separates on cooling. The white solid is dissolved in the proportion of 1 grm. in 10 C.C. of boiling 95 per cent. alcohol, 5 C.C. of water are added to the boiling solution, with a trace of animal charcoal, and the hot solution is filtered quickly. The p-nitrobenzyl chloride crystallises in white needes, melting-point 99" C.The preparation of the nitro- benzyl esters of the organic acid must be carried out in a common solvent of the bromide and the salt of the acid, for which purpose a mixture of 2 volumes of 95 per cent. alcohol and 1 volume of water, generally described as 63 per cent. alcohol, is usually most suitable. A boiling mixture of 10 C.C. of alcohol and 5 C.C.of water readily dissolves 1 grm. of the nitrobenzyl bromide which remains in solution, pro- vided it is kept hot; it contains sufficient water to dissolve 1 grm. of the sodium or90 ABSTRACTS OF CHEMICAL PAPBRS potassium salt of almost any organic acid a t the ordinary temperature, and will retain in solution the resulting sodium or potassium bromide even at 0" C. The reaction is carried out in a flask by boiling under a reflux condenser for one hour with monobasic acids or two hours with dibasic acids.In preparing the salt by the neutralisation of an acid, the solution should be left slightly acid, since a trace of alkali in excess would produce ethyl esters. Systematic recrystallisation of the products from diluted alcohol is carried out until a constant melting-point is obtained. The following well-characterised esters are described : Formate, m.-pt.31" C. ; acetate, m.-pt. 78" C.; propionate, m.-pt. 31" C.; butyrate, m.-pt. 35" C.; benzoate, m.-pt. 89" C.; o-toluate, m.-pt. 90.7" C.; o-nitrobenzoate, m.-pt. 111-8" C.; o-chloro- benzoate, m.-pt. 106" C.; anthranilate, m.-pt. 205" C. ; p-bromobenzoate, m.-pt. 139.5" C.; 2,4-dinitrobenzoate, m.-pt. 142" C. ; phenylpropiolate, m.-pt. 83" C.; thio- cyanate, m.-pt. 85" C. ; oxabte, m.-pt. 204" C. ; malonate, m.-pt. 85.5" 42. ; tartrate, m.-pt. 163" C.; citrate, m.-pt. 102" C. J. F. B. Influence of Carbohydrates on the Accuracy of the Van Slyke Method in the Hydrolysis of Casein. E. B. Hart and B. Sure. ( J . Biol. Chem., 1916, 28, 241-249; through J .Soc. Chem. I d . , 1917, 36, 158.)-The presence of carbo- hydrates during the hydrolysis of casein by the Van Slyke method brings about a total redistribution of the amino-acids, and this varies with the nature of the carbo- hydrate. The redistribution is particularly marked in the hexone bases, and a decided loss of amino-nitrogen also takes place when the protein is hydrolysed in the presence of xylan.The method of direct hydrolysis is, therefore, unreliable when applied to the determination of amino-acids in feeding stuffs; owing to the varia- tion in the nature and quantity of the carbohydrates in feeding stuffs, it is impossible to establish factors of correction for the results. Use of Diphenylamine and Diphenylbenzidine for Colorimetric Esti- mation.L. Smith. (ZeitscA. a d . Chm., 1917, 56, 28-42; through J. SW. Chem. Id., 1917, 36, 165.)-The intensity of the colour obtained with di- phenylamine in the colorimetric estimation of nitric acid (compare Tillmanns, ANUYST, 1911, 36, 67) is largely influenced by shaking the tube, excessive shaking causing a diminution. To obtain reliable results, therefore, shaking should be avoided, the necessary mixing being done by moving a suitable stirrer a few times up and down in the tube, and then allowing the liquid to remain at rest for the pre- scribed period of one hour.It is suggested that the observed phenomenon is due to the formation of a volatile substance during the oxidation of diphenylamine, the presence of hydrogen chloride being also a determining factor.The stability of the colour is a t a maximum a t ordinary temperatures. The sensitiveness of the reagent depends largely on its composition, and for the estimation of the follow- ing amounts of nitric anhydride per litre the annexed formulae are recommended: 0-1-3.0 mgrms. ; 0-04 grm. diphenylamine, 39 C.C. water, concentrated sulphuric acid to 100 c.c.; 0.5-10.0 mgrms.; 0.04 grm.diphenylamine, 26 C.C. water, and sul- phuric acid to 100 c.c.; 100-25 mgrms.; 0.08 grm. diphenylamine, 20-5 C.C. water,ORGANIC ANALYSIS 91 and sulphuric acid to 100 c .c. amine as a reagent for nitric acid, but its sensitiveness is somewhat greater. Diphenylbenzidine behaves analogously to diphenyl- Importance of the Varrentrapp Reaction in Fats and Oils. W. Schrauth.C'hern. Eng. and Manufaxtzcrer, 1916, 24, 203-204.)-Although hydrogenation in the presence of a catalyst is the usual modern method of converting un- saturated fatty acids into saturated ones, it seems possible that some of the older processes could be carried out on a commercial scale with the means now available. This applies especially to the Varrentrapp reaction, in which oleic acid is converted into palmitic acid by fusion with an excess of an alkali hy- droxide : Cl,H,,COOH+2NaOH=C,,H,lCOONa+CH,COONa+H~.The reaction is not confined to oleic acid; all unsaturated acids may be converted into saturated acids of lower carbon content. The following are the details of the process as applied to whale oil: 2,500 kilos. of the whale oil fatty acids are placed in an autoclave of 5,000 litres capacify, 800 kilos.of sodium hydroxide dissolved in an equal quantity of wat,er are added, and the mixture is heated a t 260" C. for six hours. The pres- sure must not be allowed. to exceed 10 atmospheres. The resulting mass, which is quite free from the objectionable odour of whale oil, may be worked up into a soap, or the fatty acids may be liberated and distilled.The yield of fatty acids so ob- tained is about 85 per cent. of the quantity taken originally. The hydrogen liberated during the reaction may be collected and utilised. w. P. s. Estimation of Free and Combined Sulphur in Vuleanised Rubber, and the Rate of Combination (of Sulphur with Different Types of Plantation Para Rubber. B. J. Eaton and F. W. F. Day.(J. Xoc. Chem. Ind., 1917,36,16-20.)- The vulcanised rubber is crumbled between small creeping rollers, and a representa- tive portion is selected and carefully picked over under a lens for " skin," insuffi- ciently crumbled particles, etc. ; 0.1374 grm. portions are then wrapped in filter- paper packets and extracted for about 100 hours with boiling acetone in a Beadle and Stevens apparatus (fhALYST, 1913, 38, 143); three times during the extraction the packets being opened and their contents teased out.When the extraction is completed, the estimation of the sulphur by combustion is made as soon as possible. The packet is placed in a glass tube 3 cm. long and 1 cm. in diameter, sealed at one end; this is inserted in i) combustion tube with the open end forward and about 8 cm.from the front end of the tube. This end of the tube is connected with two test-tubes, the first containing 1.5 C.C. and the second 0.2 C.C. of 7N sodium hy- droxide solution ; these tubes may also be connected with two small tubes containing 2N sodium hydroxide solution. Dry oxygen is passed through the apparatus while heat is applied, and as soon as the paper begins to char, the current is increased to about 400 C.C.per minute until ignition occurs. The current is then reduced, and regulated to produce a sinall bright flame with as little smoke as possible. The com- bustion takes about fifteen minutes. The contents of the absorption vessels are mixed, treated with bromine in hydrochloric acid, and the resulting sulphuric acid is precipitated as barium sulphate.The free or soluble sulphur is estimated in the acetone extract. The residue is heated with nitric acid and bromine under a92 ABSTRACTS OF CHEMICAL PAPERS reflux condenser, then evaporated to dryness, the residue heated with a mixture of fusion mixture, potassium nitrate, and potassium chlorate, the mass dissolved, the solution acidified, and the sulphuric acid precipitated with barium chloride. Experiments with three different types of Para rubber showed that the rates a t which they combined with sulphur wits in accordance with their different rates of cure as estimated by their physical properties (load-stretch) . The percentage of combined sulphur a t the optimum time of cure was practically the same for all three types, and was always about 4 to 4.5 per cent. calculated on the mixing (90 per cent. rubber and 10 per cent. sulphur). w. P. s.