MEANS OF DETERMINING THE QUALITY OF MILK. 605 
without much trouble, and in a short time, the comparative 
richness of milk, is still a desideratum. The practical diffi¬ 
culty which has attended the employment of the several 
methods of milk-testing^ hitherto in use, is to be attributed 
in some measure to the fact that upon any scale that can 
be devised, on any principle whatever, there is not one 
point to which we can refer as a standard of purity. The 
nearest approach we can make to the establishment of such 
a standard is to ascertain, by experimenting on several spe¬ 
cimens of average quality and known purity, whether we can 
seize upon some physical property which admits of suffi¬ 
ciently accurate measurement for the purpose. It has been 
ascertained that an inferior quality is indicated when the 
specific gravity is below a certain range—but this can be 
raised artificially by the abstraction of some of the cream; 
an inferior quality is also indicated when the per-centage of 
cream is less than a certain number; but the instrument em¬ 
ployed for exhibiting this per-centage is found to be falla¬ 
cious, inasmuch as it only shows how much cream has floated 
to the surface in a given time, and experiment has proved 
that the richer the milk the less is the cream disnosed to 
i 
float. Many persons are able to judge pretty accurately as 
to the quality of milk, by carefully observing the transparency 
which the fluid exhibits when poured in a thin film from 
one vessel to another; and it would appear that this pro¬ 
perty, which has already suggested the instrument of M. 
Donne, might be again turned to account in the construction 
of a more simple instrument, which would indicate definitely, 
and thus enable us to register numerically, the degree of 
transparency possessed by a given sample; and we should be 
then in possession of a very efficient means of estimating the 
degree to which the milk has been diluted, or how far it fell 
short of the average quality. 
Such an instrument has lately been invented; the prin¬ 
ciple of its construction is extremely simple, and the experi¬ 
ments instituted with a view of testing its performance, several 
series of which have been repeated, appear to have been 
attended with the most satisfactory and encouraging results. 
The instrument is made of brass, in the form of a shallow- 
oblong vessel, capable of containing about an ounce of fluid : 
the depth of the vessel is made to increase gradually, by 
means of a slab of white enamel fixed in a gentle slope from 
one end to the other : this slab is graduated throughout its 
entire length. Upon this the milk is poured till the vessel 
is filled, and a cover of plate glass is then put on—this should 
be done bv giving it a sliding motion to exclude air-bubbles. 
xxxiii. 6 2 
