156 THE LACTATES, AND UREA AS IT EXISTS IN URINE. 
tent, in this acid. Let us now return to the artificial prepara- 
tion of lactate of urea. 
To obtain this preparation in a direct manner, we begin by 
obtaining the lactic acid from lactate of lime. To this end, 
100 parts of lactate of lime, pure and dried at 120°, is dissolved 
in 200 parts of hot water, holding in solution 41 parts of pure, 
dry crystals of oxalic acid. This solution, when filtered, rep- 
resents, in every 100 parts, 75 of pure lactic acid; 73 
parts of pure dry urea is now to be added, the solution filtered 
and evaporated at a low heat, and crystallization effected in the 
usual modes. 
It is, nevertheless, preferable to prepare lactate of urea by 
double decomposition, either by treating oxalate of urea by 
lactate of lime, or by acting on sulphate of urea with lactate 
of baryta. We should here make some observation on these 
two salts of urea, reserving, for the end of the essay, some ge- 
neral remarks upon the salts of this base, which our researches 
have afforded us an opportunity of studying. 
The oxalate of urea has been described by Berzelius. It 
is composed of urea 62.56, and of oxalic acid 37.44, in the 100 
parts. It is obtained by combining 10 parts of urea with 60 
parts of oxalic acid, heated to 120°. The mixture is dissolved 
in 6 or 800 parts of hot water, filtered and carefully evaporat- 
ed to a pellicle, when the oxalate crystallizes in a mass formed 
of prismatic needles, interlaced together, or in pearly tears. 
This salt may likewise be obtained by acting with oxalic acid 
on the product of the concentration of urine deprived of its 
salts. It is evident that in this case the oxalic acid decom- 
poses the lactate of urea naturally contained in the urine ; this 
oxalate is to be concentrated and purified with animal char- 
coal and crystallized. 
The sulphate of urea is procured by mixing 100 parts of 
oxalate of urea with 125 parts of pure silky sulphate of lime ; 
a small quantity of water is added, and heat applied for a few 
moments ; four or five volumes of alcohol of 36° is added, the 
liquid filtered and evaporated ; the residue is the sulphate of 
urea in granular or needle-shaped crystals, of a sharp and pun- 
