American Milk- Condensing Factories. 
Ul 
it is advantageously boiled with reduced pressure, at a low 
temperature. Syrups are evaporated, as in the refining of sugar, 
in vacuum pans, or vessels in which the atmospheric pressure 
may be partially taken off by air-pumps. A low degree of heat 
only is thus required, producing economy in fuel, and avoiding 
tlie risk of over-heating and burning the syrup. With these 
well-known principles in mind, dairymen will be able to see 
the advantages obtained by Mr. Borden in using the vacuum pan 
in expelling the water from milk. It will be observed, too, 
that from the moment the milk enters th^ pan, it is protected 
from various harmful influences, such as dust, flies, and other 
insects, which are liable to be caught in the liquid, when eva- 
poration is carried on in an open vessel, as under the Provost 
method. 
In Europe, and, indeed, in theUnited States, until quite recently, 
vacuum pans have been formed of copper ; but owing to the high 
price of this metal, the temptation is to make them as thin as 
possible ; and the collapse of the pan, owing to the external atmo- 
spheric pressure, is not an unfrequent occurrence. In America 
the substitution of cast iron has, in a great measure, obviated 
this difficulty. I am told that the cast-iron pans for condensing 
milk are employed with quite as much success as those made of 
copper, and Fig. 3, on the next page, is an illustration of an iron 
pan, showing one of the best forms of construction in this material. 
The engraving shows three coils of pipe, but, for condensing 
milk, generally but one — the lower coil in the pan — is used, 
and the coil is arranged to run round the inside surface of the 
pan rather than across the pan, as in the figure, in order to 
facilitate cleaning. I am indebted to the Technolorjist, for the 
illustration and description of its parts. The drawing is well 
arranged to give a good idea of the manner in which solutions of 
sugar, and other organic substances, may be evaporated at com- 
paratively low temperatures, and I deem it important to a clear 
understanding of what I shall have to say with regard to the 
preparation of condensed milk. 
The pan A (Fig. 3) is of any size, from 4 to 10 feet 6 inches 
in diameter, and is cast in four pieces : A^ being the bottom, 
A^ and A^ shells, and A* the dome-piece. B is the dome, con- 
nected by the vapour-pipe C, to the catcher D, the latter being 
a cylindrical vessel, divided part-way by a partition or apron, D\ 
against which, in case of boiling over, the liquor would be 
dashed, and would gather in the bottom, where the amount can 
be seen at the glass-gauge, d}, and, if necessary, emptied into the 
pan by means of the faucet and pipe d. 
From the top of the catcher D, the vapours are conducted by 
pipe E to the condenser E^, which is placed 33 feet above the 
