Dec. 1, 1864.] THE TECHNOLOGIST. 



ON CHEMISTRY APPLIED TO THE ARTS. 205 



than they shcmld contain to render their employment economical, it 

 behoves those who use large quantities in their manufacture to ascertain 

 the extent of the moisture contained in soaps. This may he pretty ac- 

 curately approximated to by placing a quarter of an oimce, divided 

 into thin shreds, upon a hob or other warm situation, and leaving it for 

 several days, when it will lose nearly the whole of the water it originally 

 contained, or about a third of its weight if it does not contain an undue 

 proportion. In many instances the proportions of alkali in soap may 

 seriously affect its applicability. Thus, I ascertained a few years since 

 that the quality of soap best adapted to clean madder purples should 

 not contain more than 5 per cent, of alkali, whilst for pinks, where it is 

 necessary to remove any loose colour which the mordants may have 

 mechanically retained, a more active soap is required, viz., one con- 

 taining from 6 to 7 per cent, of alkali. 



I have now to draw attention to a totally different kind of manufac- 

 ture, viz., that of composite, stearic, and Belmont candles. Many years 

 elapsed between the scientific discovery by M. Chevreul of margaric and 

 stearic acids, and their application to illuminating purposes, for it was 

 early in 1825 that MM. Chevreul and Gay-Lussac took out a patent 

 with a view of realising this advantage. But it was reserved for a 

 manufacturer, M. de Milly, to perfect the manufacturing details of the 

 processes, and to render these candles a marketable commodity. This 

 he effected by also improving the manufacture of the wicks, and he was 

 the first to introduce this article to the trade in 1832, under the name 

 of bougies de Tetoile. The following was his modus operandi. 100 lbs. of 

 tallow, 17 lbs. of lime previously slacked, and 1,000 lbs. of water were 

 placed in a large iron boiler, and kept at the boil for several hours by 

 means of a jet of steam. The result was that the glycerine dissolved 

 in the water, whilst the fatty acids united with the lime. The insoluble 

 stearate, oleate, and margarate of lime were then decomposed by weak 

 vitriol, under the influence of heat. Insoluble sulphate of lime was 

 produced, and the fatty acids liberated. These, in their turn, were sub- 

 mitted to hot and cold pressure which liberated the oleic acid, leaving 

 the solid stearic and margaric acids behind ; it was then only necessary 

 to cast them into moulds containing wicks, and. the bougies de Fetoileweve 

 produced. MM. cle Milly and Motard have introduced, of late years, 

 several important improvements into this branch of manufacture, the 

 most important of which is that of operating under pressure, by which 

 means they succeed in decomposing the fatty matters with 3 or 4 per 

 cent, of lime instead of 17, this of course involves the saving of a 

 large quantity of vitriol. M. Bouis has made a further improvement, by 

 adding to stearic candles 3 or 4 per cent, of sebacic acid, which is ex- 

 tracted from castor oil, and has the high fusing point of 261°. M. 

 Chevreul also suggested a simple method of increasing the whiteness of 

 these candles, by the addition of a small quantity of ultramarine blue 

 to neutralise the slightly yellow tint of the manufactured acid. One of 



