THE CARBOHYDRATES. 275 



On heating the substance on platinum foil it does not melt, but 

 ignites and burns with a bluish-green flame ; at the same time 

 a peculiar, penetrating odor develops. It does not give the murexid 

 reaction. When boiled with caustic alkali it is decomposed and 

 the sulphur liberated as a sulphide. With benzoyl chloride, in the 

 presence of an excess of caustic alkali, it forms benzoyl-cystin, and 

 is thus precipitated as a sodium salt in the form of fine lustrous 

 platelets, which are readily soluble in water, but insoluble in solu- 

 tions of the caustic alkalies. Upon the addition of an acid to such 

 a solution, benzoyl-cystin separates out as such. It is soluble in 

 alcohol and alcohol-ether, slightly so in pure ether, and almost insolu- 

 ble in water. Its needle-like crystals melt at 156-158 C. The 

 formation of benzoyl-cystin may be expressed by the equation : 



CH 3 CH 3 



| /NH 2 NH 2V | 

 2C fi H 5 .COCl + C< )C = 



Benz9yl I \g S/ I 



COOH COOH 



Cystin. 



CH 3 CH, 



| X NH(C 6 H 5 .CO) (C 6 H 5 .CO)NH | 



C< >C + 2HC1 



| \S S/ | 



COOH COOH 



Benzoyl-cystin. 



On boiling with concentrated hydrochloric acid, benzoyl-cystin is 

 decomposed with the formation of benzoic acid and cystin. 



Quantitative Estimation of the Neutral Sulphur In one 

 portion of the urine the oxidized sulphur, viz., the mineral and the 

 conjugate sulphates, is estimated as has been described. In a 

 second portion the total sulphur is then ascertained as follows: 100 

 c.c. of urine are treated with 12 grammes of a mixture of sodium 

 and potassium carbonate (11 : 14), and evaporated to dryness in a 

 platinum dish. The residue is thoroughly fused, and on cooling 

 extracted with hot water. The carbonaceous residue is filtered off, 

 washed with hot water, and filtrate and washings treated with a 

 few crystals of potassium permanganate. After heating for fifteen 

 minutes (a little more of the permanganate must be added if the 

 solution becomes decolorized), and concentrated hydrochloric acid is 

 added until the liquid is distinctly acid. It is then brought to the 

 boiling-point, treated with 20 c.c. of a hot saturated solution of 

 barium chloride, when the barium sulphate which is thus formed is 

 estimated as usual (see page 220). The difference between the two 

 results indicates the amount of the neutral sulphur. 



THE CARBOHYDRATES. 



The carbohydrates which may be found in the urine comprise 

 glucose, Ia3vulose, laiose, maltose, lactose, dextrin, animal gum, and 

 certain pentoses. Of these, traces of glucose, dextrin, animal gum, 



