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There are three principal methods of refrigerating. (1). Direct expansion. In this method
gas is expanded directly into coils of pipes placed on the walls or ceilings of the cold rooms; the pipes
become very cold, and the moisture of the air is deposited upon them in the form of snow. This
method is simple and economical, but does noi readily lend itself to providing considerable variations
of temperature, and it is therefore best suited for stores designed for one class of goods only, in which,
therefore, a uniform temperature can be maintained throughout. (2.) Brine circulation. Here the
gas expanded is used to cool brine which is circulated in pipes through the cold rooms. This
system readily adapts itself to the production of varying temperatures. (3.) Cold air blast. Here air
is cooled by being blown over a battery of pipes, in which cold brine circulates or in which gas is
being expanded, and the cooled air is drawn through the storage rooms. This system is cheap and
has come largely into use of late years. Inasmuch as the moisture is removed from the air by
cooling it, there is risk of the very dry atmosphere causing damage to certain kinds of goods.
Moreover, the air is apt to take up odours, and being distributed throughout a cold store may give
the flavour of hops to apples, or of onions to butter. Hence it has been found necessary to purify
the air, and this may be accomplished1 either by removing the frost adhering to the pipes, when
the closed system is used, or by renewing or purifying the brine in cases in which there is immediate
contact with the cold solution. On the withdrawal of an old supply of brine abundant evidence of
the extent to which it has been contaminated is afforded. Steaming was at one time practised for
strengthening purposes, but it was found that the impurities and smells of the cold air rooms were
so concentrated in the brine that nuisance was caused, and this practice has had to be abandoned.
There are two points of practical importance to which further attention might with advantage
be directed in connection with cold storage from the public health point of view : first, the
question as to cleanliness of surfaces, and, secondly, that of purity of air.
While it may be admitted that "dirt" is less likely to be productive of harm at 14° F.
than at 64° F. or 74° F., it would a priori appear essentially necessary that a room in which it is
intended that food shall be stored should be kept clean. " Cleanliness," says the Managing
Engineer of the Cologne slaughterhouse,2 " is a main desideratum in the cold store. The best
air-cooling apparatus and the most careful attention are worthless if the store is dirty, or if
pieces of flesh and fat hang about the compartments or lie on the floor. These soon become
decomposed, and spoil the whole cold-air store." This writer goes on to prescribe that " some
time every day whilst the cold store is shut the passages on the floor should be cleaned. If the
floor is properly laid it is best to swill it out. Then the water can be removed with squeegees, as is
done with asphalte pavement, to the gutters. No damage can be done by the swilling and the
consequent increased moisture in the air, since there is no raising of the temperature, in which
case the moisture might settle on the already cooled meat."
The second question—that of purity of air—has already received a good deal of attention, for
some foods continually give off gases and odours (meat is said to be the only food which " does not
gas "), and certain of the articles commonly cold-stored are specially apt to take up odours. In a
few instances, moreover, difficulty has arisen on account of use having been made, for insulation of
the cold store walls, of a preparation containing tar, inasmuch as during warm weather a tarry smell
has resulted, andgreat difficulty has been experienced in dealingwith the same; indeed, at Frankfort-onMaine
and at Cologne it was found necessary to " change the insulation" on this account. Therelative
air-purifying effect in the case of apparatus in which there is direct contact with brine, as contrasted
with apparatus in which air-cooling is accomplished by direct expansion, has been referred to. The
respective merits of the two systems are referred to in a paper by E. Stetefeld,3 from which it may
be incidentally inferred that a good deal of difficulty has been experienced in some cold air stores in
keeping down smell resulting, among other things, from a dirty condition of the storage chambers.
More attention will doubtless be directed to this question of purity of air in cold stores in the near
future.
Conclusions.
The main issue raised by the Bermondsey Borough Council in sending the report of their
medical officer to the London County Council is as to the fitness for consumption of the natural ice
brought chiefly from Norway into London. Dr. Brown in his report says it is obvious that only a
very small proportion of the ice is destined for food, and yet " any particular consignment may be
used either for drinking or for cold storage purposes." He adds that, while he does not doubt
most of the natural water from which the ice comes is perfectly pure, there is no guarantee that
villages and towns do not drain into the places whence the ice is derived. As regards the
artificial ice, Dr. Brown remarks that the water supplied in London " is presumably suitable for
manufacturing ice from as long as it it considered fit for drinking purposes." " Distilled water,"
he adds, " is, of course, the best for the purpose, though however pure the water used may be, it
will avail little as regards the purity of the ice made from it unless it is strictly guarded from
contamination during the freezing process and the subsequent handling."
These conclusions appear to me to be well-founded, and I quite agree with Dr. Brown in
thinking it undesirable to continue to repose absolute confidence in natural ice in ignorance of the
conditions which exist at the harvesting grounds. The employment of distilled-water ice was
recommended on the best authority in Germany twenty years ago and the use of artificial ice has
steadily gained ground in the United States, and is being slowly but surely extended in this
country. Having in view the nature of the risks involved in consuming natural ice, and the
1 Lessons gathered from the Working of Cold Air Stores, Joseph Musmacher.—Ice and Cold Storage,
2 Ice and Cold Storage, April, 1903.
3 Ice and Cold Storage, February, 1903.