808 EXPERIMENT STATION EECOED. 



" Cystin and tyrosin can be completely and quantitatively separated by means 

 of absolute alcohol saturated Asdth hydrogen chlorid. The tyrosin is rapidly 

 converted into tyrosin ester and goes into solution. It can be recovered by 

 boiling the solution vphen diluted with water for eight hours and then neutraliz- 

 ing with ammonia. Almost the whole of the cystin is insoluble; the portion 

 which goes into solution (perhaps cystin hydrochlorid) is precipitated by add- 

 ing an equal volume of absolute alcohol. The cystin is not converted into its 

 ethyl ester since on dissolving the insoluble portion in dilute hydrochloric acid 

 and neutralizing with ammonia the cystin is precipitated in the typical hexag- 

 onal plates." 



Determination of amino nitrogen in the tissues, D. D. Van Slyke (Jour. 

 Biol. Chem., 16 (1913), No. 2, pp. 187-195).— " The amino acids are extracted 

 from the tissues with hot water. Uncoagulated proteins in the extract are pre- 

 cipitated by alcohol. Alcohol and the slight amount of ammonia present in the 

 extract are removed by concentration in vacuum, and the amino nitrogen in the 

 residue is determined by the nitrous acid method. The rapidity with which the 

 amino nitrogen reacts with nitrous acid, and the relatively small increase which 

 it shows as the result of hydrolysis of the extract with hydrochloric acid, Indi- 

 cate that the amino nitrogen determined by the method outlined represents ap- 

 proximately the free o-amino acids. Only a few per cent of the amino nitrogen 

 appears due to proteins or their intermediate products and to amins not of 

 protein origin. The correction for the latter can, when desirable, be readily 

 determined." 



Testing' animal fat for phytosterol, M. Fritzsche (Ztschr. Untersuch. Nahr. 

 u. OenussmiL, 26 (1913), No. 11, pp. 6U-6Jt8) .—The digitonin method of Mar- 

 cusson and Schilling, while very satisfactory, requires 24 hours for its execu- 

 tion. The method has now been modified so as to require only two hours, as 

 follows : 



Fifty gm. of the melted and clear filtered fat is heated in a 150-cc. beaker 

 with 20 cc. of a 1 per cent digitonin solution to from 60 to 70° C, and stirred 

 at this temperature for five minutes with a mechanical stirring device. Fluid 

 and semisolid fats are filtered, with the aid of suction, through an easily perme- 

 able Biichner funnel holding a 50-mm. diameter filter disk. The residue is then 

 washed with ether six successive times with the aid of gentle suction. 



While still warm the solid fats are treated, after the stirring process, with 

 20 cc. of chloroform, filtered under pressure, and washed twice with 5 cc. of 

 warm chloroform and six successive times with 5 cc. of ether aided by slight 

 suction. The fat-free residue (digitonin) with the filter disk is dried for five 

 minutes on a watch glass at from 30 to 40°, and after the removal of the filter. 

 The residue is transferred to a dry test tube provided with a cooling tube and 

 heated with 2 cc. of acetic acid anhydrid to liquefaction with a small flame and 

 then heated five minutes longer. The hot fluid is filtered through cotton into a 

 crystallizing dish and the test tube and funnel washed twice with 0.5 cc. of 

 warm absolute alcohol. The residue is then dried upon the water bath aided 

 by a current of air, 1 cc. or less of absolute alcohol is added, covered with a 

 watch glass, heated to solution, co<^)led, and the solution, etc., poured after 

 crystallization has set in, upon a porous clay plate. When the mother liquor 

 has been absorbed, the crystals are transferred to a crystallization dish. 



A small portion of the crystalline mass is heated on a watch glass ten min- 

 utes at 70° and then employed for the melting point determination. The re- 

 mainder of the residue is dissolved in absolute alcohol and used for a second, 

 third, and possibly a fourth determination. Parafiin when present does not 

 affect the results. 



Some tests with beef tallow, oleomargarin, lard, and butter are included. 



