Abidity in Milk, 
57 
propel* concluct of dairying that those who have to handle milk 
should be able, not only to recognise the presence of acidity in 
it, but also to estimate with some approach to accuracy the degree 
of acidity which a given sample of milk or its products may have 
reached. 
The chemist has for a long time been able to do this with 
as much precision as can be desired in any ordinary process of 
the kind ; but the application to dairy-work of the method which 
he employs, though simple enough in theory, involves practical 
obstacles of such a nature that in the difficulty which has been 
found hitherto in dealing with them must be sought the ex- 
planation of the fact, that although cheese-makers especially 
have for years past been appealing to the chemist for aid in 
helping them to determine the acidity of milk and whey, the 
chemist has hitherto, in this country at any rate,' made no re- 
sponse to their appeal. In the course of the experimental in- 
quiries which the writer has for the last few years been carrying 
on in dairying, it became at an early stage evident to him that a 
mode of estimating acidity with fairly approximate accuracy was 
of the first importance ; and he has made a large number of ex- 
periments with the view of working out a process which, whilst 
accurate enough for practical purposes, should be so simple as 
to be usable by any person of ordinary intelligence. Before 
proceeding to describe the process itself and some of the results 
which are obtainable from it, it may be well to say a few words 
on the principles on which it is founded. 
First, then, with reference to the measurement of acidity 
generally. If we take a vessel containing any acid liquid, such 
as vinegar, we can measure the volume of the vessel by means 
of a foot-rule ; we can also estimate its weigJit by putting it into 
the scales ; and we can determine its temperature, if we wish to 
do so, by means of the thermometer. But how are we to gauge 
its acidity ? We ordinarily test ' sourness ' by the taste ; but a 
little reflection, or still better, a little experiment, will soon 
convince anyone who needs conviction that the sense of taste, 
like all the other senses, is liable to serious error, and that it is 
therefore quite incapable of giving information of any precision 
or trustworthiness. Most dairyers, however, who have any pre- 
tensions to a proper knowledge of their business are aware that 
better information as to acidity than the sense of taste or smell 
can give them may be obtained by the use of litmus-paper. If 
' The process of acidimetry suggested in the following pages is similar in 
general details to that proposed by Soxhlet and Henkel, but the appliances 
employed by these authorities are far more complicated, and, in the writer's 
opinion, quite unsuited to ordinary dairy use. 
