Lecture on Milk. 
417 
of about 50^, a longer time than twenty-four hours will not add appre- 
ciably to the quantity separated. But though the bulk of the cream 
be not increased, it may become denser when the temperature is 
increased. In comparative experiments, therefore, an equal tem- 
peratm-e should be maintained. 
The two kinds of lactometers might be used together with advantage : 
cue to measiu-e the amoimt of cream, and the other to take the density 
of the skimmed milk. When large quantities of milk have to be sup- 
plied to workhouses or public institutions, it is very desirable to have a 
ready mode of testing its quality. It might be so ai'ranged that, when 
the milk comes in, some of it should be placed in graduated tubes, and 
at the end of twenty-fom* hours the skimmed milk could be drawn oS, and 
a float put into it. This float might be so constructed as to give the 
proportion of water in the milk from 10 to 12 per cent. I intend to 
make a nmnber of analyses of milk piu-posely mixed with water, and 
to construct a set of two instruments for testing the quality of milk. 
When the ordinary lactometer, which measm'es the amount of cream 
in the milk, is used, practical difiiculty is experienced in removing the 
cream. You might do it with a pipette ; but unless you have a very 
steady hand indeed you cannot get all the cream oft' : at any rate the 
servants in a large establishment could not be expected to do it. I 
have, therefore, thought of using an instrument similar to the alcali- 
meter of Dr. Moore, analytical chemist of Coblentz. It is a very 
haudy instrument, which is frequently used in chemical laboratories,, 
consisting of a graduated tube divided into one hundi'ed parts, eacK 
of seven grains content, the whole being the himdredth part of a. 
gallon. You ^vill by this means get a proportionate part of a gallon^ 
The milk is filled in, and then left for fom'-and-twenty hours. The 
cream rises, and can be readily let oft" in this manner. [The Professor 
gave a practical illustration with the apparatus.] The specimen 
before me contains no less than fifteen measures, a large amount of 
cream. If in London milk you get eight or nine measm-es of cream, 
you must be satisfied : very frequently you will get only seven, and 
even six. In this instrument the sMm milk is prevented from flowing 
out by means of a clasp, and an Indian rubber tubing at the bottom, 
which, being pressed, allows the skim milk to flow off, so that the 
cream gi-adually descends without a pai'ticle escaping. I am at 
pi'csent occupied in the endeavoiu' to ascertain if cream is of a imiform 
comijosition when gathered in this way. If it is so, then we might 
form some idea of the amount of butter that a given quantity of milk 
should produce. There is one other lactometer, or milk-tester, which 
is simply a graduated cylinder, in which the milk is kept from the 
influence of the atmosphere. In other respects it resembles the 
graduated tube ; but all the tubes in which graduation begins at the 
top have this practical inconvenience, that the skimmed milk cannot 
be removed. Of late I have been endeavomring to ascertain whether 
the size of the tube affects the quantity of cream which is thrown up, or 
whether it makes any appreciable difference. As far as I have gone, 
trying tubes of three sizes, I do not find any difference in the volume. 
These insti-uments and investigations, which assume very varied 
aspects, wiU continue to occupy my attention. 
VOL. XXIII. 2 E 
