24 THE JOURNAIv OF PHARMACOLOGY. 



ary to observe the amount of chlorides excreted daily ; a disappearance 

 would give rise to alarm, while a gradual daily increase would rather 

 justify the expectation of a favorable outcome. It would be well if urine 

 were more often examined relative to its per cent, of chlorides than it is. 

 Exudative inflammations, particularly those with exudation into a serous 

 cavity, cause a diminution in the excretion of chlorides, because in these 

 conditions the exudate contains, as a rule, a liberal quantity of chlorides 

 as well as other salts. In many cases of albuminuria, resulting from a 

 diseased condition of the kidneys, chlorides are excreted in diminished 

 quantity. In the course of many chronic diseases the quantitative estima- 

 tion of chlorides is of great importance, for the reason that the facts so as- 

 certained, serve as a clue to the activity of the digestive apparatus. 



Detection of chlorides. — Usually the silver nitrate test is employed. If 

 much albumin is present, it must first be removed. A small quantity, 

 however, does not interfere. Silver nitrate precipitates phosphates and 

 carbonates, as well as chlorides. It therefore becomes necessary, before 

 applying the reagent, to add a few drops of nitric acid ; this keeps the dis- 

 turbing elements in solution. Silver nitrate produces a white, curdy pre- 

 cipitate with chlorides. This precipitate is readily soluble in ammonia 

 water, but is reprecipitated upon addition of nitric acid. 



Quantitative estimation. — Before a quantitative estimation of chlorides 

 can be made, any albumin which is present must be removed. This may 

 be done in the manner already stated (see albumin).* 



Methods employed : 



I. Volhard' s method. — This method is based on the fact that when a so- 

 lution of potassium sulphocyanate is added to an acid solution of silver ni- 

 trate, containing a little ferric sulphate, a precipitate is formed, as follows : 



AgNOs + KCNS = AgCNS + KNO3. 



Simultaneously a red coloration is noted, caused by the formation of 

 ferric sulphocyanate. 



Fe2(S04)3 + 6KCNS=Fe2(CNS)6 + 3K2S04. 



At first this red color again disappears, the ferric sulphocyanate reacting 

 with the silver nitrate. 



Fe^CCNS)^ + 6AgN03 =6AgCNS + FeaCNOs)^. 



The red color only remains permanent when all the silver has been pre- 

 cipitated in the form of silver sulphocyanate. 

 Solutions required. 



A. — AgNOgV.S. Prepared by dissolving 16.955 grammes of chem- 

 ically pure silver nitrate in enough distilled water to make, at or near 15° 

 C, exactly icoo cc. 



