THE JOURNAL OF PHARMACOLOGY. 25 



B. Solution of ferric alum [(NH4)2Fe2(S04)4 -{- 24H2O], saturated in 

 the cold. Freshly prepared when wanted, 



N 



C. — KCNS V.S. Prepared by dissolving 10 grammes of chemically 



pure potassium sulphocyanate in 1000 cc. of distilled water. This solution 



is too concentrated, and must be adjusted so as to correspond with the 



N 



— AgNOs V.S., cc. for cc. This may be conveniently done by following 



directions given in the U. S. P. (see Volhard's Solution) 10 cc. ( i 



decinormal silver nitrate solution together with 0.5 cc. of ferric ammonium 



sulphate T. S. (U. S. P.), and 5 cc. of diluted nitric acid, are placed in a 



flask. The sulphocyanate solution is added to this'mixture, from a burette, 



in small portions at a time. A white precipitate of silver sulphocyanate is 



formed after which the red color of ferric sulphocyanate begins to appear. 



This however disappears upon shaking the flask, as long as any silver 



nitrate remains present, unchanged. When all the silver is converted into 



sulphocyanate, a single additional drop of the potassium sulphocyanate 



solution produces a red color which cannot be made to disappear upon 



shaking, but which imparts a perceptible tint (reddish) to^the contents of 



the flask. Now note the number of cc. of the potassium sulphocyanate 



solution used and make the adjustment accordingly. 



Example : Say 9.8 cc. of the potassium sulphocyanate solution were 



required. Then 980 cc. of the solution would have to be diluted to 1000 cc. 



N 

 in order to correspond to a — V.S. After diluting, a new trial should be 



made, when a given volume of the one solution must correspond to the same 

 volume of the other. It is w^ell to note the depth of the tint to which the 

 volumetric solution is adjusted, so that when used for volumetric assays, 

 the same tint may be attained. 



Execution of the method: 10 grammes of albumin free urine are placed 

 in a flask or beaker of about 150 cc. capacity, and 20-30 drops of pure 30^ 

 nitric acid are added together with 2 cc. of ferric alum solution. If the 

 sample of urine is very dark in color, so that it would be difficult to dis- 

 tinguish the end reaction, it is advisable to first add 3-4 drops of a strong 

 solution of potassium permanganate (1-30), shaking thoroughly. This 

 will generally cause most of the color to disappear. Now add from a 

 burette a definite volume of the silver nitrate solution, being sure this is in 

 excess. (About 30 cc. wdll generally suffice.) Add distilled water to 

 make 100 cc. and mix thoroughly. Filter through a dry filter, and by 

 means of a pipette remove 50 cc. of the filtrate. Titrate this with the 

 decinormal potassium sulphocyanate solution until a faint, but permanent, 

 reddish tint is attained. The number of cc. of decinormal potassium sul- 

 phocyanate solution used are multiplied by two and the product deducted 



