290 THE URINE. 



On boiling with concentrated hydrochloric acid benzoyl-cystin is 

 decomposed with the formation of benzoic acid and cystin. 



On shaking cystin in alkaline solution with /9-naphthalin-sul- 

 phochloride (dissolved in ether) and subsequently acidifying with 

 hydrochloric acid (after removal of the ether) a precipitate of 

 /9-naphthalin-sulphocystin is formed, of the composition C 26 H 24 S 4 N 2 O 8 . 

 This dissolves with difficulty in water and cold absolute alcohol, 

 but readily in hot absolute alcohol ; from the latter the substance 

 crystallizes out in flat, partly bent needles, which at 215 C. (uncor- 

 rected) decompose with the formation of a brown oily material. 



Isolation bf Cystin from the Urine and Quantitative Estimation. 

 To this end Abderhalden has recommended the following method, 

 based on the principle just outlined. The entire amount of urine 

 of twenty-four hours is filtered and the residue washed with 

 ammonia. The filtered urine and the ammonia washings are 

 united. 500 c.c. (best after previous concentration in the vacuum 

 at 40 C.) are then treated with 4 c.c. of normal sodium hydrate 

 solution and then shaken for six to eight hours with an ethereal 

 solution of 4 grammes of /3-naphthalin-sulphochloride. At in- 

 tervals of one and a half hours 3 c.c. of the alkali solution are 

 further added. At the expiration of the shaking the ether layer 

 is removed and the aqueous solution oversaturated with hydro- 

 chloric acid. The resulting precipitate is filtered off and after 

 decolorization with animal charcoal crystallized from hot absolute 

 alcohol. The crystals are dried at 100 C. and weighed. 1 gramme 

 of the compound corresponds to 0.35 gramme of cystin. 



Normal urine gives no precipitate with /9-naphthalin-sulphochlo- 

 ride, or a slight turbidity only. 



Preparation of Cystin from Albumins. For purposes of study 

 cystin is most conveniently obtained from human hair as follows : 

 500 grammes of hair are boiled for four hours with 1500 c.c. of 

 hydrochloric acid (specific gravity 1.19). On cooling, concentrated 

 sodium hydrate solution is carefully added until the reaction is 

 nearly neutral (not alkaline). Animal charcoal is added in excess ; 

 the mixture is boiled for about three-quarters of an hour and 

 filtered while hot. On cooling, impure cystin separates out. This 

 is collected on a filter, dissolved in hot dilute ammonia, and repre- 

 cipitated by the addition of glacial acetic acid. The resulting pre- 

 cipitate is again dissolved in a small amount of hot dilute ammonia, 

 the solution is filtered, when on spontaneous evaporation of the 

 ammonia the cystin separates out in rosettes composed of the typical 

 hexagonal platelets. These can be further purified by a repetition 

 of the precipitation of the ammoniacal solution with glacial acetic 

 acid. The crystals are finally washed with water, alcohol, and 

 ether. 



Quantitative Estimation of the Neutral Sulphur. In one portion 

 of the urine the oxidized sulphur, viz., the mineral and the conju- 

 gate sulphur, is estimated as previously described (page 238). In a 



