388 Dr. E. W. Davy on a new and simple Method of 



volume of gas found : : 0-2 : to the required quantity of urea ; 

 or multiplying the first and third terms by 5, we have 1-549 

 cubic inch of gas representing one grain of urea, which is a 

 simpler proportion. Using these data, I made several compara- 

 tive experiments on different samples of urine with my method 

 and that of Baron Liebig^s, which I believe is considered one of 

 the most accurate of the methods of determining urea in urine 

 at present known. The following are the results of three com- 

 parative experiments on different samples of urine, using the 

 same with each method. 



Amount of urea in grains and parts of a grain in one fluid ounce 

 of urine. 



Liebig's. New method. 



Ist experiment . . 3-680 3-712 



2nd experiment . . 5-328 5-472 



3rd experiment . . 4-976 4-976 



In the first and second experiments the quantity of common 

 salt present in the iirine was taken into account, as it is found 

 to increase to a slight degree the apparent quantity of urea in 

 the urine by Liebig's method. In the third this was not taken 

 into consideration, and the quantity of urea was compared with 

 the mean of two results obtained by my method. These experi- 

 ments show how very closely the results obtained by the new 

 method agree with those by Baron Liebig's, and therefore show 

 the correctness of the former method. 



I prefer the hypochlorite of soda to that of potash as a decom- 

 posing agent, because the soda salt is an article of ovir pharma- 

 copoeia under the name " Sodse chlorinatse liquor,'' and therefore 

 can be so easily procured ; whereas the potash salt, not being 

 used in medicine, would require to be specially made for the 

 pui-pose. As to the hypochlorite of lime, I do not think it so 

 effectual, and it has the disadvantage of soiling the sides of the 

 graduated tube by the carbonate of lime formed in the reaction. 



In reference to the quantity of hypochlorite of soda to be 

 employed, it should always be used in excess ; and I think that 

 about five or six times the volume of the urine employed would 

 be found generally to be quite sufficient, and ensure there being 

 an excess of the hypochlorite. The amount required may be 

 easily determined also by direct experiment, by adding to a cer- 

 tain quantity of urine to be examined in a glass a measured 

 quantity of the hypochlorite, and leaving it for a short time till 

 the evolution of gas is nearly over ; then if, on the addition of 

 more of the hypochlorite, the effervescence is renewed, it shows 

 that there was not enough of the decomposing liquor first em- 

 ployed, and more must be added from time to time till no further 



