Miscellanies. 38 1 



larger moulds, but to rival, in perfection, the beauty of cut glass. 



Nov 



3. Pasteboard roofs. — Roofs of out buildings in Holland have 

 been covered with pasteboard cut into squares, and dipped repeated- 

 ly in boiling tar, until thoroughly covered and impregnated with it 

 and then dried in the sun. The pieces are then placed smoothly on 

 the roof, lapping at the edges, and fastened with nails. It is stated 

 that these roofs are a great security against dampness, and that they 

 last longer than shingles, — Bib. Univ. Nov., 1832. 



4. On saponaceous vegetables. — A report was made, by M. Bus- 

 sy, on a root long employed in Persia and the East for cleaning cash- 

 mere shawls and other stuffs. Several French manufacturers have 

 also used it for years with much advantage. They call it Saponaire 

 d'Egypte. It probably belongs to the genus Gypsophila, very analo- 

 gous to Gypsophila Struthium. This root, when reduced to pow- 

 der, occasions violent sneezing, like Euphorbia and certain acrid 

 resins. 



It communicates to water, by decoction or even by mixture, a 

 particular softness and unctuosity, and the property of frothing like 

 soap without occasioning too great viscosity. This quality is ascer- 

 tianed to reside in various degrees in several plants. It depends on 

 the presence of a peculiar substance, which causes water to lather 



by agitation. 



The bark of Quillaia saponaria which is sold in the public markets 

 in Peru, as a substitute for soap, is remarkable for this property. 



When soap is added to water, there is, in addition to the solvent 

 power of the water, the chemical action of the alkali of the soap, 

 but this is much less important than is generally supposed, for in soap 

 the alkaline properties of potash and soda are almost entirely neutral- 

 ized, by the acids of the fat. Simple alkaline solutions, either caustic 

 or carbonated, we know will not well answer as a substitute for soap. 

 The action of alkalies or of soap, in common washing, is not there- 

 fore, simply to saponify the greasy or resinous matters with which the 

 cloth is impregnated, but only to render them miscible in water, not 

 soluble, but miscible, that is, to bring them into such a state of divis- 

 ion as to occasion their easy and free suspension in the water as oil 

 is suspended in milk of almonds, or butter in milk. Every substance 

 which increases the viscosity of water, produces this effect, such as 



Vol. XXIV.— No. 2. 49 



