LINSEED OIL INDUSTRY, The. In the commercial world there are known at the present time a number of vegetable oils, which in the raw state and without the aid of chemi cals are capable of absorbing the oxygen of the air to a greater or less degree and becom ing solid. These are commonly called °drying oils.° By far the most valuable to commerce, both as to usage and results obtained, is linseed oil, expressed from the seed of the plant Linum usnatissimum, the common flax. In early times the object of its cultivation was principally for the flax fibre. Although the great economic importance of linseed oil, due to the large increase of manufactured products in which it is used, has been of but compara tively recent years in this country, the seed or plant bears the hall mark of great antiquity. It is positively known that drying oils had been discovered prior to the Christian era, and, though uncertain, it would seem reasonable to assume that linseed oil was among them. For centuries it appears that the oil's greatest characteristic, its wonderful drying properties, was given little attention. It was not until the 12th century, when oil painting was discov ered, that we may say a true appreciation of the essentially exclusive properties of linseed was felt, and from that day to this it is the only oil that has successfully satisfied all the require ments of oil painting.
In earlier years the small amount required, principally by the artists, was produced by little, if any, apparatus, and often in the studio. Later, the oil began to find en larged fields of usefulness, and the crudest of mechanical apparatus was devised for its manu facture. With such appliances, however, oil could be produced only at an excessive cost, and its use on a broad commercial basis was not feasible. Indeed, up to within comparatively recent years the invention and improvement of linseed oil machinery has been slow, and in fact to the United States may be attributed the greater part of the advance made in this indus try in the past 100 years. The earliest method recorded for the production of linseed oil is a receipt by Theophilus, a monk writing in the 12th century, and which becomes particularly interesting when we find that the treatment of the seed or method was almost identically the same as it is to-day. °Take linseed and dry it
in a pan without water, on the fire; put it in a mortar and pound to a fine powder; then re place it in the pan, and pouring a little water on it, make it quite hot. Afterward, wrap it in a piece of new linen, place it in a press used for extracting the oil of olives, of walnuts, or of the poppy, and express it in the same manner.° It will be seen from the above that the seed was treated separately four times, as follows: Dried, crushed, cooked and pressed. With the exception of the drying, which is not necessary, the plan of procedure to-day is the same. Dur ing the intervening years, however, many dif ferent methods have been used as well as dif ferent kinds of machinery.
In the making of linseed oil there are two very essential steps which must be carefully watched; the first is the crushing or grinding of the seed; the second is the cooking or °temper ing° of the ground seed. In the proper manipu lation of these two processes rests a crusher's ability to make a good yield of oil. Heat and moisture are of the greatest importance in pro ducing the best yields; we find, in fact, that many times the ground seed or meal was pressed entirely without cooking. Oil made in this manner was called °cold pressed° oil. In the cold process the oil expressed is beautifully light in color and heavy in body; furthermore, upon boiling to a high temperature the oil does not darken but becomes lighter, and after mix ing with the varnishes is perfectly clear and without sediment. On the contrary, oil made from the tempered meal is thinner and darker in color; on boiling at high temperatures it darkens still more, and throws down a quantity of white and greasy precipitate. Owing to the light yield of oil in the cold process, however, the cost is excessive and little is now made.