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work being included in the item of miscellaneous expenses. Fishermen were not included in the census, and it is possible that a larger proportion of the salted fish was prepared in connection with the actual catch than at the census of 1900, thus accounting in part, at least, for the decrease in the quantity.

IMPORTANCE OF CANNING AND PRESERVING INDUSTRIES.

CANNING AND PRESERVING FRUITS AND VEGETABLES, AND FISH AND OYSTERS.

COMPARATIVE SUMMARY-CENSUSES OF 1904 AND 1900.

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1 Decrease.

2 Exclusive of fruits and vegetables valued at $715,920, fish at $274,403, and oysters at $12,900, manufactured by establishments classified as food preparations, pickles, preserves and sauces, slaughtering and meat packing, wholesale, etc.

Importance of the Industry. The importance of the canning industry is not to be measured solely by its commercial extent. The principle of the conservation of food products by sterilization or pasteurization is of immense significance in the nutrition of man. It enables nourishing foods of a perishable character to be kept and transported to great distances and to be used in localities where fresh foods of similar kinds are otherwise unobtainable. Such preserved foods mean everything to pioneers, explorers, armies, and navies. The "winning of the west" in the United States has been marked by the débris of the rusty cans. The roads along which the pioneers who settled the great American desert marched since 1865 have been bordered with the discarded packages in which they carried their foods.

It is doubtless true that foods when they can be had fresh are to be preferred to those which have been sterilized. It is also true that many unsterilized foods from unsanitary environments are more dangerous in the fresh state than when they have been exposed to a high temperature. Taking into consideration all the circumstances in the case, it must be conceded that the process of sterilization, first practiced by Appert and afterward placed on a scientific basis by Pasteur, has proved of almost immeasurable advantage to mankind. Thus for this greater reason the character and quality of foods thus preserved should be wholly above suspicion, and no adulteration or sophistication of any kind should be practiced therewith. The manufacturer is quite as much interested as the consumer in placing the whole output of sterilized foods on a plane above suspicion.

PART VII.

VEGETABLE OILS AND FATS, AND NUTS.

VEGETABLE OILS AND FATS.

The production of a substance known as fat or oil, composed of oxygen, hydrogen, and carbon in the form of a fatty acid and combined with glycerine, is a function of almost every plant. The fat acids are usually in combination with glycerine, which plays the part of a base and in so far as its proportion by weight is concerned is much less important than the fatty acid itself. In round numbers it may be said that nine-tenths of all glycerids or fats are composed of a fatty acid and one-tenth of glycerine. When at ordinary temperature this combination is in a liquid form it is called an oil, and when at ordinary temperature it is in a solid or semi-solid condition it is known. as a fat. The term "ordinary temperature" means in this connection that of an ordinary living room and not the extremes of outside temperature. In general terms it may be said that the temperatures referred to are included between the minimum of 50 degrees and the maximum of 85 degrees F. In so far as chemical composition and dietetic properties are concerned, there is no distinction between the oils and the fats. The names are simply a means of ordinary discrimination which has assumed importance by reason of common usage.

There are three of the fatty acids which are particularly important from a dietetic point of view which go to make up the greater part of these fatty and edible vegetable oils and fats. These three acids are oleic, stearic, and palmitic. Of the three, cleic acid is by far the most important, as it constitutes the greater part of nearly all these bodies, especially of oils. In fact the term "olein" and oil are of common origin. Palmitic acid exists chiefly in certain forms of vegetable oil and fats, while stearic acid is a very important constituent of animal oils and fats.

These three acids uniting with glycerine form the glycerids which make up the great body of edible and animal oils and fats, and these principal glycerids are known as olein, palmitin, and stearin, respectively.

Chemical Characteristics.-The chemical composition of these bodies has been pointed out above. There is, however, in almost all cases, some

free acid present in the compound, that is, an acid which is present uncombined with the glycerine. This free acid is usually present in small quantities and is more abundant in the overripe and older plants than in the freshly matured parts. The natural oil also contains certain other ingredients which may be regarded as impurities, and which it is necessary to remove from the oils by a process of purification or refining before they are ready for the table. These impurities may be of a mechanical nature, that is, consisting of parts of the material itself from which the oil is expressed or of certain juices not oils which are found in the animal tissue, portions of protein and other forms of nitrogenous matter, and traces of carbohydrates and gums. The oils have certain definite chemical reactions which are common to them as a class. Among these may be cited, principally, the faculty of absorbing, under certain conditions, the halogens, namely iodin, bromin, and chlorin.

Without entering into any technical description of this process it is sufficient to say here that the degree of absorption of iodin is in a measure the test for the varieties of oil. The different vegetable oils have, as a rule, certain definite relations to the absorption of iodin by means of which they may be to a certain extent identified or separated from similar bodies. The degree of absorption is expressed in the percentage by weight of the oil itself and is known as the iodin number. If, for instance, a gram of any particular oil absorbs one gram of iodin, it is said to have an iodin number of 100. Many oils absorb more than their own weight of iodin, while many others absorb very much less. Another characteristic of oil is found in the fact that with certain reagents, such as an acid either in a dilute state or in a concentrated state, definite colors are produced which are characteristic of the variety of oil in question. As an example of this may be cited the faculty which cottonseed oil has of reducing nitrate of silver to the metallic state, leaving the silver in that finely divided form which has a black color. This is the only oil in common use which has this faculty, and hence it may be regarded as a characteristic test.

Another characteristic chemical property of cottonseed oil is the color which is produced in the Halphen reaction, which has already been described.

One of the most valuable chemical properties of oil is the amount of heat which is produced when it is burned. Inasmuch as oils in relation to their food value are useful chiefly for the production of animal heat, this chemical property becomes of great hygienic and dietetic significance. Of all classes of food products the oils and fats have the highest calorific power. If, for instance, it is said in general that one gram of carbohydrates, such as sugar or starch, on complete combustion will yield 4,000 calories, one gram of protein 5,500 calories, then one gram of oil or fat will yield 9,300 calories. The fats and oils vary among themselves in respect of the number of calories yielded, but all of them give, approximately, the number last mentioned. It therefore

DRYING AND NON-DRYING VEGETABLE OILS.

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follows that oils and fats are the most valuable constituents of food in respect of the production of heat and energy.

Crystalline Characteristics.-The forms of crystals which the fats assume on solidifying are valuable indicators of the nature of the oil. While these crystal forms are not in all cases distinct, yet they are influenced to a greater or less extent by the nature of the oil itself. Thus the presence of any particular oil may very often be ascertained by the examination of the crystals produced by lowering the temperature very slowly or by dissolving the oil in a volatile solvent and gradually evaporating the solvent. Tests of even greater delicacy may be obtained by first saponifying the fat or oil, separating the fatty acid, and subjecting it to crystallization.

Distribution of Oils in Plants. In nearly all cases the part of the plant which contains the most oil is the seeds. In fact all of the vegetable oils which are used for edible purposes are extracted from the seed of the plant. In the case of olives the meaty portion around the seed yields the edible oil of highest value, but in all other cases of edible oils they are derived from the seeds themselves. It is a mistake to suppose that the seeds are the only parts of the plant that contain oil. It is found in all parts of vegetable substances, but is usually concentrated in the seed. It is rather an interesting fact to know that in the seeds of plants both the protein and fats or oils are found, as a rule, in a highly concentrated state, while the carbohydrates are not found chiefly in the seed itself, that is the germ, but distributed in the fleshy envelope surrounding it or in roots or tubers.

The oils and fats are almost all soluble in ether and petroleum ether, though there are some exceptions to this, as in the case of castor oil, which is also insoluble in petroleum ether or gasoline. On the contrary, oils and fats, as a rule, are not soluble in alcohol, but the fatty acids derived from them are. Castor oil is also an exception to this rule, since it is quite soluble in pure alcohol.

Drying and Non-drying Vegetable Oils.-It might be supposed that if one vegetable oil be edible they all would be. This would probably be the case if vegetable oils were all composed almost exclusively of the three classes of glycerids, which have been mentioned above, but such is not the case. There are other fatty acids in combination with the glycerids which exist in vegetable oils, and chief among these may be mentioned linoleic acid, which exists in considerable quantities in the oil of flax seed, and gives to it its valuable property of a drying oil which makes it so useful in the manufacture of paints. Whenever vegetable oils and fats contain any especial quantity of linoleic acid, or any other fatty acid which has drying properties, they are rendered more or less unfit for human consumption. The number of drying oils is very great, but the most important are linseed oil, hempseed oil, and poppyseed oil. Other vegetable oils have, to a certain degree, drying

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