178 BASIC BODIES. 



the most important question regarding its constitution still remains 

 unexplained, namely, in which form or combination the sulphur is 

 contained, in the cystine or in this adjunct. The chemical investi- 

 gations regarding cystine, which have been hitherto instituted, do 

 not tend to support any hypothesis. 



Combinations. Hydrochlorate o/c?/s#me,C 6 H 6 NS 2 O 4 .HCl, crys- 

 tallises without water in plates grouped in a star-like form. Berze- 

 lius* obtained the combination with bichloride of platinum by 

 direct union; this salt is not crystallisable; it dissolves easily in 

 water and alcohol, but is insoluble in ether. 



Nitrate of cystine, C 6 H 6 NS 2 O 4 .HO.NO 5 + HO, crystallises 

 readily, losing its one atom of water at 85. 



Preparation. Urinary calculi, in which cystine occurs, are dis- 

 solved in a solution of potash, and the cystine is precipitated from 

 this solution by acetic acid ; or we dissolve them in ammonia, and 

 allow the filtered fluid to evaporate in the air. 



Tests. Cystine is characterised by the readiness with which it 

 crystallises in well-formed hexagonal plates, which may be distin- 

 guished with great ease under the microscope, and by its solubility 

 both in alkalies and mineral acids. Further, it may be known by 

 the peculiar odour which it developes on dry distillation and on 

 burning, which is unlike that evolved by any other similar substance. 

 Liebig has given the following test for cystine. The potash-extract 

 of the substance in which we are searching for cystine must be 

 decomposed with a solution of oxide of lead in caustic potash; if, 

 on the application of heat, there be a precipitation of sulphide of 

 lead, cystine is probably present; we must, however, previously 

 satisfy ourselves that no other sulphurous body, as, for instance, 

 mucus, albumen, &c. be simultaneously present. 



If cystine be mixed with a small quantity of the urates, the two 

 substances may be separated by the aid of boiling water, in which 

 the former is insoluble. Uric acid occasionally appears under the 

 microscope in the form of hexagonal tablets, but we should never 

 trust in these cases to microscopic examination alone. 



Physiological Relations. 



Occurrence. Cystine was originally discovered by Wollaston,f 

 in a urinary calculus. Calculi of this nature, although very rare, 

 have since been found by many other chemists, as, for instance, 

 Prout, Taylor, Baudrimont, Lassaigne, Dranty, Civiale, Buchner, 



* Jahresber. Bd. 27, S. 631. 

 t Phil. Trans., 1810, p. 223. 



