238 ANNUAL OF SCIENTIFIC DISCOVEKY. 



glycerine: 1st. Its solvent action approaches that of dilute alcohol more 

 nearly than that of distilled water. 2d. In general those bodies are most 

 soluble in glycerine which are most soluble in alcohol. 3d. In most cases 

 the solvent power of alcohol is superior to that of glycerine; in some 

 others their power is nearly equal, and in the case of strychnia, it possesses a 

 greater solvent action. It must also be remembered that glycerine adds .to 

 any compound of which it forms a part, nothing but innocent, if not softening 

 and sedative properties, whereas alcohol has very active properties, which, in 

 certain cases, would be very injurious. 



COAL-TAR A:NT> ITS PRODUCTS. 



At a recent meeting of the London Society of Arts, Mr. Grace Calvert gave 

 the following somewhat detailed account of the substance known as coal-tar, 

 and the many and curious products which science, within the last few years, 

 has extracted from it : Coal-tar, as is well known, is the product left in gas- 

 works in the condensers, being formed with the gas from coal, and afterward 

 deposited from the gas upon cooling. This substance was generally sold to 

 the tar distillers, who obtained from it a volatile fluid called coal naphtha, a 

 light oil, composed principally of carbonic acid and a heavy oil of tar, a solid 

 substance, called pitch, being also left in the retort. Coal-tar has of late yeara 

 been used in paving. When this substance, together with tar and asphalte, 

 is heated, and poured while in a liquid state upon gravel, between the inter- 

 stices of the paving stones, the whole is bound together so durably, as not to 

 require repaving for several years. There is, however, this important sanitary 

 advantage connected with this plan, namely, that no impure matter nor stag- 

 nant water can percolate through this impervious pavement and collect be- 

 neath, giving forth noxious effluvia, to the injury of the health of the inhab- 

 itants. This pitch, when submitted to distillation in retorts, yields a porous 

 but at the same time a dense coke, and the oils distilled in the operation can 

 be employed to advantage for lubricating machinery. Coal-tar has also been 

 applied, when mixed with gutta-percha or India-rubber, to insulate telegraph 

 wires, and prevent metals from being acted upon by the atmosphere. One 

 of the first products which comes over in the distillation of tar is a mixture 

 of very volatile hydro-carbons, which has received the name of crude naphtha, 

 and this, when again distilled, is sold under the name of naphtha. When it 

 is intended to apply this product to more particular purposes, it is purified by 

 mixing it with 10 per cent, of its bulk of concentrated sulphuric acid ; and 

 when the mixture is cold, about 5 per cent, of peroxyd of manganese is added, 

 and the upper portion submitted to distillation. The rectified naphtha found 

 in the receiver has a specific gravity of 0'85. This substance is used to dis- 

 solve caoutchouc. Eectified naphtha is also used for mixing with wood 

 naphtha, to render the latter more capable of dissolving resins for the produc- 

 tion of cheap varnishes. This rectified naphtha, submitted to a series of 

 further purifications, has received from the eminent French chemist, named 

 Pelouze, the name of "benzoin" or "benzole," which has the property of re- 

 moving with great facility spots of grease, wax, tar, and resin, from fabrics 



