Ether is alcohol, two molecules deprived of H_{2}O [alcohol, C_{2}H_{5}O HO; ether, (C_{2}H_{5})_{2}O]. Distilling spirit of wine and sulphuric acid together, it seemed obvious that the sulphuric acid should possess itself of the H_{2}O, and leave the ether. But on this theory it was not possible to explain the invariable formation of sulphovinic acid (a sulphate of ethyl) in the process, nor the simultaneous distillation of water with the ether. Williamson proved that the acid first combined with the alcohol molecule, setting the water free, and that then an excess of alcohol decomposed the sulphovinic acid thus formed into free sulphuric acid and ether, this circuit proceeding continuously. SPIRIT OF NITROUS ETHER. This popular medicine has been traced back to Raymond Lully in the thirteenth century, and to Basil Valentine. But the doctor who brought it into general use was Sylvius (de la Boe) of Leyden, for whom it was sold as a lithontryptic at a very high price. It first appeared in the P.L., 1746, as Spiritus Nitri dulcis. In English this was for a long time called “dulcified spirit of nitre,” and in the form of sweet spirit of nitre still remains on our labels. In the P.L., 1788, the title was changed to Spiritus Ætheris nitrosi, and in that of 1809 to Spiritus Ætheris nitrici. The process ordered in the first official formula was to distil 6 oz. (apoth. weight) of nitric acid of 1·5 specific gravity, with 32 fluid oz. of rectified spirit. Successive reductions were made in the proportion and strength of the acid in the pharmacopœias of 1809, 1824, and 1851, to 3½ fluid ounces of nitric acid, sp. gr. 1·42, with 40 fluid ounces of rectified spirit, and a product of 28 fluid ounces. The object of these several modifications was to avoid the violent reaction which affected the nature of the product. ETHIOPS. Æthiops or Ethiops originally meant a negro or something black. The word is alleged to have been derived from aithein, to burn, and ops, the face, but this etymology was probably devised to fit the facts. There is no historical evidence in its favour. Most likely the word was a native African one of unknown meaning. It became a popular pharmaceutical term two or three hundred years ago, but is now almost obsolete, at least in this country. In France several mercurial preparations are still known by the name of Ethiops. There are, for instance, the Ethiops magnesium, the Ethiops saccharine, and the Ethiops gommeux; combinations of mercury with magnesia, sugar, and gum acacia respectively. These designations echo the mysteries of alchemy.