determining the amount of Urea in the Ui-inary Sea-etion. 387 



much longer, even for a day if convenient, and having set the 

 experiment going, it requires no further attention ; and when 

 the decomposition is completed, it is only necessary to measure 

 the quantity of gas produced by transferring it into a graduated 

 tube or measure. 



I have generally used a graduated tube in the first instance, 

 as it saves the trouble of transferring the gas and incurring the 

 risk of losing some of it in the process. That which I would 

 recommend as being convenient for this purpose is a stout tube 

 having a bore of half an inch in diameter, and capable of hold- 

 ing from 2 to 3 cubic inches. A tube having this bore and 

 about 14 inches in length, will hold 3^ cubic inches, which will 

 be quite large enough. Eacb cubic inch of it should be divided 

 into tenths and hundredths of a part of a cubic inch. 



It is scarcely necessary to remark, that in cases where great 

 accuracy is required, due attention must be paid to the tempera- 

 ture and atmospheric pressure, and certain corrections made if 

 these should deviate from the usual standards of comparison at 

 the time of reading off the volume of the gas ; but in most cases 

 sufficiently near approximations to accuracy may be obtained 

 without reference to those particulars. From a number of expe- 

 riments, I have ascertained that the quantity of gas evolved from 

 different amounts of urea, treated in the way I have just de- 

 scribed, very closely approximates to the quantity of nitrogen 

 gas which should be furnished from the urea by calculation. 

 This will be seen from the following, taken from many experi- 

 ments. 



The fifth part of a grain of urea should furnish by calculation 

 0'3098 parts of a cubic inch of nitrogen gas at 60° F. and 30' 

 bar. ; the same quantity of urea treated as described furnished in 

 one experiment 0'3001, and in another 0'3069 parts of a cubic 

 inch of gas at the same temperatm-e and pressure ; which shows 

 that the calculated quantity of nitrogen differs from the amount 

 of nitrogen gas obtained by only a few thousandths of a part of 

 a cubic inch. I may observe that I was obliged to operate on 

 such small quantities of urea, on account of the graduated tube 

 I had at the time being only of one cubic inch capacity. 



Seeing, then, that the quantity of gas evolved agrees so very 

 closely with the calculated amount of nitrogen present in a cer- 

 tain quantity of urea, 1 take the calculated amount as being the 

 more correct; and knowing the relation that exists between a 

 certain quantity of urea and nitrogen, I can from the quantity 

 of gas evolved in any case easily calculate the amount of urea 

 present by the simple process of rule of three. Thus the fifth 

 part of a grain, or 0-3 of a grain of urea, gives by calculation 

 0*30y8 parts of a cubic inch of nitrogen gas. Then 0-3098 : the 

 3 1) 2 



