62 
Acidity in Milk. 
for measuring the Neutraliser and the means by which the 
process of measuring is to be effected. After a great deal of 
experimentation it has been decided to adopt the drop as the 
simplest form of unit, and one which can be measured with 
sufficient precision for the purpose in view, provided certain 
simple precautions are observed. Those precautions ai'e the 
use of a dropper with an outlet of standard size, and the regu- 
lation of the rate of dropping to aloid one drop per second.^ 
The latter condition can be easily observed by anyone of 
ordinary intelligence ; the foi'mer is satisfied by always using 
the same dropper. With the view of providing a dropper which 
may be used by various persons so as to give comparable results, 
the writer has adopted a nickel-plated brass tube having an 
external diameter of 17 B.W.G. (Birmingham Wire Gauge), as 
being as convenient as any for the purpose. And in order to 
allow of the neutralising solution being employed in the sim- 
plest possible way, a glass pipette, having a section of the above 
tubing attached to one end and an indiarubber capsule at the 
other, by pressure on which the pipette can be filled or emptied, 
has also been adopted. 
But the most difficult element of the problem was to devise 
a receptacle for the Neutraliser in which it could be kept without 
exposure to the air, and from which it could be extracted so as 
to be measured in drops. Various forms of burette and drop- 
bottle have been tried, but all of them were found to be open to 
objections of one kind or another, from which the writer, 
believes that a simple device which suggested itself to him is 
free. This consists in fixing what may be called a glass well- 
tube in an air-tight manner in the neck of the bottle holding 
the Neutraliser, in such a way that the bottom of the tube 
nearly reaches to the bottom of the bottle, and is constricted to 
such an extent that the metallic tube of the dropper just » fits 
into it and projects for about half an inch below, when the 
dropper rests in the well-tube. By this device no air can enter 
the bottle except to supply the place of the solution as it is 
drawn off, and thus the total volume of air wliich can come into 
contact with the solution, so long as the well-tube is kept fixed 
in the neck of the bottle, is limited to the cubic capacity of the 
bottle itself ; and this limit can, obviously, only be reached when 
the solution is quite exhausted. The amount of error which 
' The variations in weight of water dropped from the same outlet as quiclcly 
and as slowly as possible may amount to nearly ten per cent., but a slight 
variation from the rate above indicated produces such a trifling error that it 
may be disregarded. 
