Experiments were made, and with these the name of Dr. Paul Dvorkovitz will ever be associated, and it was found that by the passage of a current of gas over the surface of this intermediate product, the gas caught up as it were a richness which materially increased the lighting power of the gas. To cut a long, but highly interesting, story short, this solar or gas oil was subsequently introduced by Dr. Dvorkovitz to England for gas enrichment purposes, and the extent of its employment to-day may be judged from the fact that the United Kingdom regularly imports between 60,000,000 and 70,000,000 gallons per annum for the enrichment of the coal gas which finds useful employment in practically every home throughout the land. As is known, the gas companies have to produce gas of a certain lighting quality, and it is in the upholding of the lighting strength of the gas that solar oil to-day plays so important a part. At first, the oil came almost exclusively from Russia, but now the competition from the United States has secured for our American friends the vast bulk of the trade, which, as I have shown, has reached enormous proportions. Solar oil is also largely utilized for the production of refined perfumery oils, which are quite colourless and inodorous, while the finest quality is used in pharmacy and known as _paraffinum liquidum_, and is in much demand, but in this connection it is the Russian petroleums that have gained distinction. It was held for many years that such tasteless and colourless oils could not be produced from the United States petroleums, but from the commencement of the European War, and the consequent closure of Russia’s export port, whereby all overseas trade in Russian petroleums was held up, much progress was made in the manufacture of tasteless medicinal petroleums in the United States, such articles having now become popular throughout the world. One of the most important discoveries made during recent years has been the finding of large quantities of toluol in petroleum. This article is necessary for the manufacture of high explosives. In Borneo heavy petroleum, toluol exists to a very large extent, and it was its discovery and consequent use by the allies--thanks to the offer made to the Governments by Sir Marcus Samuel, Bart.--that almost unlimited quantities of high explosives were manufactured. Vaseline is another useful commodity which is derived from the refining of crude petroleum, and this article is turned out of the American refineries as well as those of Russia and Galicia, in large quantities, but, beyond mentioning this fact, no useful purpose would here be served by relating the various processes employed. With reference to the methods generally adopted in the refining of the products from the distillation of the Scottish oil shales, these are briefly dealt with in the chapter devoted to the Scottish oil industry.