18 Dr. A. Leared on the presence of Sulphocyanides [June 17, 



distilled water was filtered through animal charcoal. The filtrate was 

 tested with the iron solution. There was no reaction whatever. 



It was plain from this that animal charcoal possesses the power either 

 of separating sulphocyanides from their solutions or of decomposing them. 



Various other methods for separating the colouring-matter were now 

 tried with more or less success. The most perfect of these, as regards 

 the removal of colour, was the addition of a solution of sub-acetate of 

 lead. But the use of this solution is open to the objection that acetate of 

 iron, which is formed in testing for sulphocyanic acid, is itself red. It is 

 true that the colour is not so intense as that which was actually formed in 

 most cases ; and it was possible in estimating the amount of the essential 

 colouring-agent present by an easy application of the colour-test to deduct 

 the amount of colour due to the acetate of iron. 



A modification of the method employed by Professor Harley for sepa- 

 rating the colouring-matter of the urine, for the purpose of obtaining 

 urohsematin, proved on the whole the best. It consists in evaporating the 

 urine in a water-bath to the consistence of thick syrup, treating with alcohol, 

 and adding gradually milk of lime. The filtrate from this mixture was 

 found to be of a light-yellow colour, closely resembling that of the iron 

 solution. The ferric solution was added to this filtrate so long as pre- 

 cipitation of oxide of iron occurred. The liquid now assumed a reddish 

 colour, varying in depth according to circumstances. The mixture was 

 then filtered ; but it generally happened that, after standing some hours, 

 a second filtration was necessary. 



The coloured fluid obtained by either of these methods from evaporated 

 urine is of a bright red colour, exactly resembling that formed by an 

 aqueous solution of sulphocyanide of potassium with perchloride of iron. 

 In some respects the two solutions did not exactly agree. 

 The colour of an aqueous solution of sulphocyanide of iron is only 

 affected by mineral acids when in considerable excess. But the colour 

 formed with iron in evaporated urine is easily destroyed by these acids. 



The colour of the pure solution is removed by perchloride of mercury, 

 while that of the organic solution is not affected by the mercurial solution. 



It is well known that in certain cases the presence of organic matter in 

 solution greatly modifies chemical action. The action of acids in the 

 present instance was a question of degree. The colour was removed from 

 the urinary solution by a small quantity of a mineral acid, and it was 

 removed or impaired in case of a pure solution by a greater quantity of 

 acid. 



The following observation throws light upon the action of perchloride 

 of mercury in the respective solutions. 



Perchloride of mercury at once destroys the colour of an aqueous solu- 

 tion of sulphocyanide of iron. But, as I have ascertained, if the solution 

 has been previously boiled (and boiling was employed in the case of the 



