ON MILK AND ITS ADULTERATION. 
185 
varied circumstances, and purposely adulterated with, known 
quantities of water, I may state that milk may be considered 
rich when it contains from 12 to 12^ per cent, of solid 
matters, 3 to 3J per cent, of which are pure fatty substances. 
If it contains more than 12 \ per cent, of solid matter, and in 
this 4 per cent, or more fat, it is of extra rich quality. Such 
milk throws up from 11 to 12 per cent, of cream in bulk on 
standing for 12 hours at 62° F., and has a specific gravity 
varying from 1*028 to 1*030. 
Good milk of fair average quality, as has been stated 
already, contains from 10 1 to 11 per cent, of dry matter, and 
in this about per cent, of pure fat. It yields 9 to 10 per 
cent, of cream and has a specific gravity of about 1*030. 
Poor milk contains 90 per cent, or more water and has a 
lower specific gravity than 1*027. Such milk yields not more 
than 6 to 8 per cent, of cream. 
Skimmed milk throws up still less cream, has a bluer colour, 
and is more transparent, and when undiluted with water has 
a slightly higher specific gravity than new milk. 
Good skimmed milk has a specific gravity of about 1*033, 
and poor skimmed milk 1*028 to 1*030. 
Milk purposely watered yields only 5 to 6 per cent, of 
cream, and invariably has a lower specific gravity than 1*025. 
If milk is both skimmed and watered it yields less than 
4 per cent, of cream, and possesses as low a specific gravity 
as 1*025 to 1*026. 
A great many experiments have led me to the conclusion 
that within certain limits the specific gravity is the most 
trustworthy indicator of quality, and that for all practical 
purposes an ordinary hydrometer float, by means of which 
the gravity of liquids can be ascertained with precision, 
and a graduated glass tube, divided into 100 equal degrees, 
constitute the safest and readiest means for ascertaining the 
quality of milk so far as it is affected by the relative propor- 
tions of the normal milk constituents. 
A set of such instruments or lactometers, one being a 
graduated glass tube for measuring the proportion of cream 
thrown up on standing, and the other a gravity float or 
hydrometer, with plain printed directions for use, can be 
obtained from Messrs. Negretti and Zambra at the cost of a 
few shillings. 
In using these lactometers no chemical skill whatever but 
only ordinary care and intelligence are required on the part of 
the operator, and as the practical indications of these instru- 
ments are perfectly reliable, Messrs. Negretti and Zambra's 
lactometers can be confidently recommended to managers 
of country lunatic asylums, workhouses, hospitals, public 
VOL. V. NO. XIX. O 
