Acidity in Alilh. 
61 
line solutions wliich are best adapted for use as neutralisers, viz. 
caustic potash and soda, when exposed to the air become gradu- 
ally weakened by absorption from it of carbonic acid, and the 
stronger these solutions are the more rapidly do they absorb 
this gas. This is, of course, fatal to their trustworthiness for 
measuring purposes, and they would be useless for such purposes 
unless they were protected from exposure to the air. In the 
laboratory this is easily effected by the use of devices which 
present no difficulty to those who are accustomed to handle 
delicate apparatus, and who can easily satisfy themselves whether 
from any accident the neutraliser solution has undergone dete- 
rioration. But for the comparatively rough pui-poses of the 
dairy, and for use by operators who would, in most cases, have 
had little or no training in the employment of such resources, 
appliances of this type would be altogether unsuitable. 
Hence the problem further resolves itself into devising an 
arrangement in which a solution of a caustic alkali, of such 
strength as to be sufficiently delicate for practical requirements, 
can be kept with so little exposure to the air as not to materially 
affect the uniformity of the results which it will give. This 
arrangement must be of such a kind that a measured quantity 
can be easily drawn from it ; and it must be, further, sufficiently 
simple to enable any person of ordinary intelligence to use it 
without risk of serious error ; sufficiently strong to prevent it 
from being easily broken ; and sufficiently cheap to make its 
cost no reasonable ground of objection. 
Having thus endeavoured to explain the principles on which 
the method of measuring acidity is based, and the conditions which 
have to be satisfied in order to make it available for ordinary 
dairy requirements, it only remains to describe the specific form 
and strength of neutralising solution, and also the unit of measure- 
ment which the writer has adopted. The Keidraliser is a 
solution of potassium hydrate (caustic potash) of such a strength 
that one unit volume exactly neutralises one volume of a 
solution of 7-87o grammes of pure, dry, crystallized oxalic acid in 
one litre of water. This solution of oxalic acid is exactly one- 
eighth the strength of the normal solution as emploj'ed for ordi- 
nary laboratory purposes, and it has been adopted because it 
has been found by a good deal of practical experimentation to 
represent an alkaline solution of convenient strength for general 
dairy work. A higher or a lower standard of alkalinity might 
be employed without affecting the principle of the test ; but 
either step is attended with disadvantages, which increase in 
proportion as we diverge from the standard above indicated. 
A more important consideration is the unit to be adopted 
