LOW TEMPERATURES AND REFRIGERATION—MARCHIS. 217 
cumstances. Even in the case of meat preservation it makes a dif- 
ference whether the meat is frozen, that is to say, immunized, or 
whether it is merely refrigerated (brought to a temperature between 
zero and 4° C.), where it is more particularly subject to the action of 
harmful germs. It also makes a difference whether it is a military 
storehouse, where the meat is only taken out for immediate consump- 
tion and the refrigerating chambers are closed up to the time the food 
is removed, or whether it is a commercial storehouse, where the meat 
is taken in or brought out daily and is more or less exposed to the 
air, and where the frequent entries of the workmen carry in noxious 
gases and impurities. In this latter case the spray evaporator 
appears preferable on account of the purification and asepsis of the 
air of the chambers. In the first case, however, the dry evaporator, 
on account of its greater simplicity and the lowering of the con- 
centration of the brine, presents some real advantages. 
It is not sufficient only to produce cold; the cold must be conser- 
vated. For this reason the insulation from heat should be considered 
a question of the first importance in the construction of a cold store. 
The proper conservation of the contents demands that the tempera- 
ture of the storage chambers should be as constant as possible. The 
question of insulating materials, therefore, has been a subject of 
particular attention by the congress. 
A good heat insulator should fulfill the following conditions: 
(1) It should be a very poor conductor of heat. If a very thin 
layer of the insulator is sufficient to obtain proper insulation, the result 
is both economy of space and economy of the insulating material. 
(2) It should have a low specific gravity. This condition is impor- 
tant in insulation installment aboard ship. Its importance is not less, 
however, in cold-storage warehouses, because of the reduction of cost 
in transporting it to the work and the possibility of economy in the 
cost of construction by making possible the construction of very 
lightly built buildings. 
(3) The insulator should be free from odor, and not subject to 
decomposition, even when moist. This condition is all important in 
the construction of cold-storage houses designed for the preservation 
of foodstuffs. These absorb very easily bad odors arising from the 
fermentation of insulating material and become unfit for consump- 
tion. For this reason such substances as rice husks, cut straw, oat 
husks, or cork mixtures made with fermentable substances, such as 
casein, should be rejected. 
(4) The insulating material should absorb to as great a degree as 
possible the bad odors which are set free in refrigerating chambers 
and render them less harmful. From this point of view peat or turf 
sometimes is of great service. 
(5) The insulating material should not be hygroscopic. It should 
not absorb and retain moisture, which is capable of causing it to lose 
