142 THE EVOLUTION OF LIFE 
series not to provide liquor potasse sufficient to 
exactly neutralise the quantity of fluid in the unboiled 
state, but rather to provide it (in a closed tube) 
to the extent of two-thirds or three-fourths of this 
amount—the former being, on the whole, the safest 
proportion.! 
An illustration will make the mode of procedure, 
at this stage, clearer. If the urine to be employed 
has an acidity of 12 minims of liquor potassz to the 
ounce, then 1 ounce of it should be placed in each 
experimental vessel, and with it a liquor potasse 
tube containing 8 minims of this fluid—inserted, with 
its narrowed and bent extremity downwards. If, on 
the other hand, the urine had an acidity of 8 minims 
of liquor potassee to the ounce, and only tubes 
containing this amount of liquor potassz were at 
the time available for use, we should then have to 
place in each experimental vessel 1} ounce of the 
urine and one of these 8-minim tubes. 
When properly charged, the neck of the retort 
or flask is to be heated and drawn out to a narrow 
extremity ; after which the urine is gently boiled 
for about two minutes over a flame, great care 
being taken to avoid any waste of the fluid by 
spurting. During the continuance of ebullition 
the extremity of the vessel is hermetically sealed. 
1 There is reason to believe that conditions other than the acidity 
of the fluid may subsequently have to be taken into account, since, 
° 
although # may seem quite favourable for one specimen, in another 
3 of the amount of liquor potassze which would have been requisite 
for full neutralisation before boiling appears to produce more speedy 
results. Such, or analogous, differences may also have to be ascer- 
tained in regard to the urine of different individuals. 

