List of the principal Patents for the Preservation of Food-cont.

1807

Exclusion of air.

1

Compression of tea into tablets by means of hydraulic power. In this state it somewhat resembles the brick-tea' of the Tartars, but in this case the leaves are held together by means of sheep's or bullock's blood.

Francis Plowden Preserving butcher's meat, animal and other comestible substances, by encrusting them with essence or extract of meat, and filling the interstices with the same.

By covering meat with hot fat or hot animal jelly. Preservation in oil, chiefly of anchovies and other fish.

Preservation of fruits without sugar. The fruit is put into bottles, heated in a water-bath to 160° to 170° F. and then the bottles are filled up with boiling water and immediately corked and cemented. Thus the air is expelled and the albumen coagulated. A little alum is frequently added.

The food is cooked to some extent, put into strong glass vessels, corked, wired, and exposed for some time to the action of boiling water. Preservation of milk by evaporating it to half its original bulk, and adding some carbonate of soda.

Preservation of milk by evaporation to one-sixth of its bulk before boiling it.

Exhaustion of the air from the vessel containing the food. The vessel was furnished with a valve which allowed the air to be drawn out by means of a special apparatus.

After exhaustion carbonic acid is admitted into the vessel. An improvement on the preceding process.

Surrounds the food with a solution of salt in water, lets it out through an aperture in an atmosphere of carbonic acid, which at the same time floats in to take its place.

Exhaustion of the air and substitution of a solution of gelatine.

Employment of acetic acid vapour and carbonic acid gas.

Date.

1846

1823

List of the principal Patents for the Preservation of Food-cont.

Method and Name.

Exclusion of air. Jones and Trevethick.

Angilbert

1841 Goldner and Wertheimer.

Exhaustion of the vessel containing the raw food in an air-tight trough of water, and admitting pure nitrogen and exhausting again. Lastly, admitting nitrogen with a little sulphurous acid, and thus any remaining trace of oxygen is removed by its combination with the acid. Articles preserved in this manner will keep for several years.

The food is put with a little water into a tin case with a hole at the top. The water is made to boil actively, and the steam thus formed escaping freely by the hole, removes the air with it, the aperture being suddenly closed. Employment of a bath of muriate of lime to obtain a quicker and more regular generation of steam. This process is now commonly employed. The substance to be preserved is soldered down in canisters, a pinhole aperture being left in the lid. It is then subjected to the action of the bath at a temperature a little above 212° F. until the contents are about two-thirds cooked, and then, while the steam is escaping freely, the aperture is closed with solder. Lastly, the canister is subjected to a temperature high enough to favour decomposition, and if it shows no sign of bulging out from the generation of putrefactive gases, it is considered that the process has been effectually carried out. Hogarth and Co. Use of steam, in place of the muriate of lime bath.

CHAPTER III.

WATER AND ITS IMPURITIES.

SINCE water enters more or less into the composition of all articles of food as well as drink, and is employed in many cases as an adulterant, as, for example, in milk-to which sometimes it communicates the germs of disease-and in spirits; and, further, since Food Analysts are constantly called upon to make analyses of water, it becomes not merely necessary that the subject should be fully considered in any comprehensive work dealing with adulteration, but that the first place should be assigned it in such a treatise.

Chemically pure water consists of a definite combination of hydrogen and oxygen, and anything additional therein contained may be looked upon as foreign matter, and be regarded in the light of an impurity.

Thus viewed, there is really no absolutely pure water to be found in nature; ice, snow, rain, and distilled waters are the nearest approaches to purity, and yet they contain no inconsiderable amount of a variety of admixtures and impurities.

1. Ice water. This water, though not absolutely free from contaminations, is yet one of the purest waters in nature, owing to the very remarkable and beautiful fact, that in freezing, which is an act of crystallisation, all, or nearly all substances, or impurities, gaseous, organic and mineral, are cast out, and are to be found in the unfrozen portion of the water; the absence of the usual gases renders, however, ice water somewhat flat and insipid. A well-known illustration of this fact is afforded by icebergs, which, although formed from the sea, yet when melted consist of water in a state of great purity. Another illustration is afforded by the method adopted in northern countries to obtain salt from the sea. The water being frozen, the salt is found in the briny mother-liquor which remains, and from which it is obtained by crystallisation. We have recently come across a third illustration of the same principle in the artificial production of ice on a commercial scale, by the low temperature produced by the evaporation of ether. In this case we submitted both the ice and the water from which it was produced to analysis with the striking results given on the next page, it being understood that only a small portion of the water actually employed was transformed into ice.

Analyses of ice and the water from which it was obtained :—

2. Snow water.—It follows from what has already been said, that the water derived from the melting of snow is also soft and pure, but much less so than that obtained by the melting of ice, since many of the impurities are retained on the surface of the small and innumerable crystals of which snow is formed.

3. Rain water. It will be readily understood that rain water will in most cases be found to contain various impurities, these being taken up by it from the atmosphere in its descent to the earth. These impurities are for the most part of a gaseous and organic character, and, of course, their exact nature and quantities will vary with the condition of the air at the time when the rain falls. The principal of these impregnations and impurities are oxygen, the proportion of which sometimes amounts to 32 per cent. of the whole of the dissolved gases, or to considerably more than occurs in the atmosphere itself—namely, 21 per cent. (this difference arises from the greater solubility of oxygen in water) nitrogen, carbonic acid, ammonia, carbonate of ammonia, nitrogenous organic matter, nitrite and nitrate of ammonia and hydrochloric acid; and in towns, carbon, sulphurous and sulphuric acids, and sometimes sulphuretted hydrogen, derived from the coal fires. According to Parkes, the total nitrogen from the nitrogenous salts amounts to 0.0985 per 100,000. Boussingault found 0-4 part of ammonia in 100,000 parts of rain fallen in Paris, and 0.079 in that from the country. Barral obtained from 0·2 to 0·3 in Paris rain water. Bineau found in Lyons even as much as 3 parts in 100,000.

According to Boussingault, the average amount of nitric acid is 0.02 in 100,000. During a hailstorm he found the rain to contain 5·5, and the melted hail 8.3 of that acid, owing to the highly electric state of the atmosphere-a condition which is attended with increased oxidation. On other occasions he met with from 0·04 to 0·21 in rain water. In the country he found only from 0.004 to 0.028. Barral met with from 0.2 to 3.6 in Paris. This latter observer obtained from 0.78 to 2.2 total solids from rain water.

The following analyses of Dr. Angus Smith show the nature and the varying quantities of the principal of the contaminations to which rain water is so subject:

Rain Water.-Average Impurities per Million Parts.

Barral found 0.78 to 2-2 total solids in 100,000 parts, and Moleschott as the mean of five samples of water, per 100,000, 3-2 to 2·24 grains per gallon. But it must be remembered that rain water, which passes over the roofs of houses before being collected, or which is retained in cisterns of any kind, acquires further and especially mineral and metallic impurities, notably lead and zinc.

4. Distilled water.-By distillation water is freed from a great many of its impurities, and is obtained in a comparatively pure condition; this will vary, however, with the water from which it has been distilled; the purer the water used for distillation, the better will be the distillate. Of course any volatile constituents present in the water will pass over, and as most waters contain more or less ammoniaeither free or as carbonate or nitrite-these will be found in the first portion of the distillate, as also in some cases other volatile impurities of an organic character. Hence it is very necessary that the chemist should in all cases satisfy himself of the purity of the distilled water he uses in his laboratory, especially that required for water analysis and the employment of the Nessler Reagent.

The distillation of water is carried out on a large scale on board many ships, it being prepared from sea water. The water thus obtained sometimes contains a little free hydrochloric acid derived from the decomposition of the chloride of magnesium.

C