1905 - 6 .] Excretion of Allantoin in Thymus Feeding. 99 
has disappeared. The results with pure allantoin gave only a 
small fractional return, and with the washing the precipitate was. 
visibly disappearing. The presence of silver allantoin was demon- 
strated in the filtrate, and hence the method proved unreliable. It 
would therefore appear that the more one washes the precipitate, 
the smaller is the result, and the less one washes the precipitate, 
the nearer it approaches to a correct result, although not free from 
ammonia. 
To overcome this difficulty the following modification of 
Poduschka’s method was devised : — 
To 50 c.c. of the urine basic lead acetate was added, and the 
excess of lead was removed from the filtrate by concentrated sodium 
sulphate solution. 
Tins was filtered, and to the filtrate was added silver nitrate 
solution (5-10 per cent.), and again filtered, until no further pre- 
cipitate formed in the filtrate upon the addition of silver nitrate 
solution. 
Dilute ammonia w T as then added to the new filtrate, and the 
allantoin silver was precipitated and filtered. 
The precipitate and filter paper were then placed in an 
Erlenmeyer’s flask, with a pinch of oxide of magnesium, as in 
Morner and Sjoquist’s method, and a little water was added. This 
was placed over the steam-bath at 60° C. for f hour. 
By this modification the ammonia was liberated, and only the 
nitrogen of the allantoin was retained. Even if the allantoin 
undergoes a decomposition into urea, there is no loss of nitrogen. 
The flask and its contents were then left to cool, and the same 
flask, to avoid loss in transferring the contents to a Kjeldahl’s 
combustion flask, was used for oxidation. 
Pure sulphuric acid was then added, and the process continued 
as Kjeldahl’s method, by means of which the nitrogen was esti- 
mated and the allantoin equivalent was calculated. Deduction was 
made for the nitrogen in the filter paper and the sulphuric acid, 
and the loss in the several stages of filtration was measured and 
the final filtrate treated as an aliquot portion. 
The method of estimation by silver precipitation has been 
criticised by Salkowski (4) as one of the most difficult of reactions, 
but as carried out by me it has yielded satisfactory results. 
