Some twenty years ago and for some time afterward tung oil, as we shall in our further description term this very interesting article, came to us through English and German channels of trade, and it was scarcely ever uniform and a great amount of money was wasted before its properties became more fully known to interested parties.
At that time its production was still in the hands of the Chinese peasants exclusively, who used very crude and primitive methods for pressing the oil and bringing it to market. The method was to roast the nuts in iron pans, so that the shells would burst open and thus free the kernels. The smaller producers would pulverize these in hand mills, while the more progressive Chinaman would have a stationary colander, rotating in a stone trough driven by oxen or other animals similar to our olden time cider mills. The meal was then warmed and the oil pressed on hand presses and in order to clarify it somewhat was boiled with water and filtered through linen. Western enterprise has changed this system to more modern methods, and we now have hot pressed tung oil, as well as hot pressed linseed oil. Attempts have been made to import the nuts of the tung tree into Europe and the United States, but on account of the weight of the shells, that constitutes one-half of the total, it was nearly entirely given up again. To import the kernels only is risky, because of the rapidity with which they become rancid. Some English and American firms have finally introduced modern machinery for pressing or extracting the oil on Chinese soil, and one American firm has put up barrel factories and storehouses for handling the export on a large scale. But this fact is well known and does not require repetition here.
The nuts consist of about equal weight of shells and kernels, which latter yield, when cold pressed, 40 to 42 per cent, when hot pressed 50 to 53 per cent and in the extraction process 58 to 60 per cent by weight of oil. Hefter in his Technology, volume II, page 60, reports as the result of cold pressing in hydraulic process as follows: - Out of 100 parts by weight of nuts - First pressing, 22.36 per cent oil of straw yellow color; second pressing, 5.56 per cent oil, darker and more viscid; oil cake, 24.08 per cent, and shells, 48 per cent An analysis of kernels made by the Jardin Colonial (France) resulted as follows: - Water, 5.14 per cent.; protein, 20.60 per cent.; fat, 52.57 per cent.; extracted matter, free of nitrogen, 14.98 per cent.; fibrous matter, 2.85 per cent.; ash, 3.86 per cent.
An analysis made by the same institution of tung nut shells showed the following composition: - Water, 14.40 per cent.; protein, 2.50 per cent.; fatty substance, .04 per cent.; extracted matter, free of nitrogen, 27.62 per cent.; crude fiber, 50.64 per cent., and ash, 4.80 per cent.
Tung oil has been known to and made use of by the Chinese for centuries in a great many ways. It serves as lubricating oil, as a means to make paper transparent and waterproof. Its use as a wood preservative, especially for boats, has been practiced in China from time immemorial, and the soot produced by slow incineration serves as the basis for Chinese or India ink, while the residuum from this process is made use of in caulking of boats and as a vehicle or binder for paint. A mixture of lime, clay and sand with tung oil will produce an imitation of granite.