564 
Proceedings of the Royal Society 
"bath, having a principle believed to he new, and probably avail- 
able in many cases where the maintenance of an exact temperature 
is required. 
7. Eeference is lastly made to an investigation of the melting- 
points of certain easily accessible and purifiable chemical sub- 
stances, for which the results of the present researches have been 
utilised. The calculations are not quite complete ; but I trust to 
place, at an early date, these important constants in the hands of 
physicists. The extremely tedious work of comparing the mer- 
curial with the air thermometer will then, for a considerable length 
of scale, he in the future to a great extent avoided. 
BUSINESS. 
The following candidates were balloted for, and declared duly 
elected Fellows of the Society: — Professor J. II. Scott, Otago; Mr 
James Graham ; and Dr It. Sydney Marsden. 
Monday , 17th May 1880. 
DAVID MILNE HOME, Esq., Vice-President, in the Chair. 
The following Communications were read : — 
1. Preliminary Notice of a Method for the Quantitative 
Determination of Urea in the Blood. By John 
Haycraft, M.B., B.Sc. 
The subject of these investigations, some of the results of which 
are before the Society to-night, was suggested to me by Professor 
Carl Ludwig, and was carried out in his laboratory at Leipzig, 
where I worked with the help of his assistant, Dr Drechsel, to 
whose kindness and large knowledge of the subject I was much 
indebted. 
In this paper I shall give simply an account of the method of 
analysis, leaving for the future a record of the facts which it has 
enabled me to obtain. 
The estimation of a quantity of urea in a pure form, or in a 
