374 
HULLETIN OF THE UNITED STATES FISH COMMISSION. 
top, which extends above the ceiling so that they may be filled without opening the 
storage room. At the bottom is usually a galvanized-irou slanting gutter, into which 
the water resulting from the melting ice flows, whence it is conducted through the 
floor of the room by a short pipe, protected from the entrance of air at its lower end 
by a small drop cup, into which the brine falls and runs over at the top. In some 
fish-houses this brine, which is otherwise wasted, runs into receiving tanks, where it is 
stored and used as required in pickling fish. The ice-and-salt tanks must be cleaned 
from time to time in order to rid them of dirt and sawdust. Their capacity should be 
in proportion to the size of the room and the excellence of the insulation secured, 
and they should be large enough to render it unnecessary to fill them oftener than 
once a day, even in the warmest weather. 
The appliances used in the ice-and-salt freezers are described at length in the 
account of the processes of freezing and storage (see pp. 377-384). 
While crushed ice and common salt are generally emiiloyed as a freezing mixture, 
numerous other compounds are available. The following compilation gives a number 
of mixtures that may be employed in refrigeration, the initial point in the case of 
crushed ice or snow being 32°, and in the other mixtures 50° F. Most of these have 
as yet been employed only in laboratory practice and for certain special imrposes, 
only a few of them having been apiilied commercially on a large scale. These formulte 
are obtained mostly from Leask’s Refrigerating Machinery and its Management, pub- 
lished in London in 1895. 
Minimum 
tempera- 
ture. 
Composition. 
Parts. 
Minimum 
tempera- 
ture. 
o F. 
Sodium sulphate 
8 
o J'. 
} 
1 
} 
Hydrochloric acid 
Sodium sulphate 
1 
1 -12 
Ammonium nitrate 
5 
^ —40 
Nitric acid (diluted) 
4 
1 
Sodium phosphate 
9 
\ r> 
Nitric acid (diluted) 
4 
I 
V —18 
Snow 
3 
J —23 
} -27 
1 
Sulphuric acid (diluted) 
Snow 
g 
-25 
Hydrochloric acid 
5 
) 
Snow 
7 
j —30 
} -10 
Nitric acid (diluted) 
4 
Snow 
4 
) -50 
Calcium chloride, crystallized 
3 
\ - 3 
Snow 
3 
} -51 
J 
Pota.sh 
4 
Crushed ice or snow 
Sodium chloride 
Crushed ice or snow 
Sodium chloride 
Ammouiuin chloride 
Crushed ice or snow 
Sodium chloride 
Ammonium chloride 
Potassium nitrate 
Crushed ice or snow 
Sodium chloride 
Ammonium nitr.ite 
Ammonium chloride 
Potassium nitrate 
Water 
Sodium sulphate 
Sulphuric acid (diluted) 
„ DESCRIPTION OP MECHANICAL FREEZERS. 
It is scarcely within the scope of the iiresent paper to enter into a comprehensive 
description of the numerous systems of mechanical freezers. They are all based on 
the principle that a liquid jiassing iuto a gaseous state, or converted into a vapor, 
carries away a definite amount of heat from the objects by which it is surrounded. 
The compression system is in most general use, and consists of three operations 
following each other in rotation, and which are practically the same in all refrigerating 
machines. By means of a large compression pump, anhydrous ammonia, which is the 
gas usually employed, is compressed to a pressure varying from 125 to 175 pounds 
to the square inch. During this operation heat is developed according to the amount 
