140 THE EVOLUTION OF LIFE 

be raised to the temperature of 212° F. (100° C.) 
for the period fixed upon. As in these experiments 
I soon found that the longer or shorter duration of 
the period of boiling of the liquor-potasse tubes did 
not appreciably influence the results, they were, for 
the most part, boiled for 15’-20’ only—though in 
many cases it was much longer, and on two or three 
occasions they were boiled for two hours. Thus 
prepared, the tubes were set aside in compartments 
labelled according to the number of minims of liquor 
potassze which they contained. 
A stock of such tubes being ready to hand, ex- 
periments may be made at any time. A suitable 
specimen of fresh urine is to be taken, whose specific 
gravity is to be ascertained and whose degree of 
acidity is to be most carefully estimated. This 
latter process I have carried out by taking exactly 
one fluid-ounce of the urine and adding liquor 
potasse to it, minim by minim, from the burette- 
tube till the point of saturation is nearly reached. 
Thereafter, the alkali has been added in half-minims 
at a time, and tested between each addition with 
litmus and turmeric paper so as to make quite sure 
of the time of complete neutralisation.1. In order to 
facilitate this part of the process, I have made use 
1 It is not unimportant here to add that the test-papers which I have 
used have been those sold by Mr Martindale, of 10 New Cavendish 
Street, London. They are similar to the papers used in the wards of 
University-College Hospital. By careful trial I have ascertained that 
+ of a minim of liquor potassze in an ounce of distilled water may be 
recognised by the previously reddened litmus paper, while } of a 
minim in the same quantity of distilled water may be detected by the 
yellow turmeric paper. The latter, though less delicate, gives the most 
certain indication, especially when a drop of the fluid to be tested is 
