Vauquelin on a new Aerolite. 315 



to undergo. In other respects they are both io quite another 

 state from raw clay, since they do not contain combined water, 

 and can no longer form a paste with this liquid. 



It is icnown that porous bodies have the faculty of ab- 

 sorbing and condensing rapidly a great number of gaseous 

 substances. May it not be, because they act in this manner on 

 the carbonic acid contained in the atmosphere and in water, 

 that they have the property of accelerating the condensation 

 of certain mortars ? We may thus conceive why they produce 

 this effect with a rich lime, whilst with poor or very hydraulic 

 limes, they give no better result, than non-porous alloys ; for, 

 the mortars of rich limes owe their solidification only to the 

 regeneration of carbonate of lime, while the solidification of 

 the mortars of very hydraulic limes is independent of this 

 cause. 



To the above remarks we may add, that the English stone, 

 from which Roman cement is made, is a ferruginous marl, in 

 spheroidical concretions, called septaria or ludi Helmontii ; a 

 description of which is to be found in our common chemical 

 works. — Ann. des Mines. 



11. Analytical Examination of Touch- stone. J5^ M. Vauquelin. 



This stone, lapis lydius, is usually arranged in the works on 

 mineralogy, in the sequel of the Corneennes stones, without 

 being entirely confounded with them. (It is the schistous 

 jasper of Brogniart, and a sub-species of rhomboidal quartz of 

 Mohs.) The specific gravity of the touch-stone of M. Vau- 

 quelin is 2.465. It whitens before the blow-pipe, exhaling a 

 feeble sulphurous acid odour. The fragments which before 

 calcination are crushed on glass, afterwards scratch it easily. 

 It has no action on the magnetic needle. Acids in the coid 

 exercise no perceptible action on a mass of touch-stone ; but, if 

 we heat muriatic acid on the mineral reduced to a fine powder, 

 there is instantly disengaged a very manifest odour of sul- 

 phuretted hydrogen ; a little iron is dissolved, and the acid 

 becomes yellow. The residuum, which is considerable, seems 

 to have become blacker by this operation. 



The alkalis easily dissever the principles of touch-stone. 

 With potash the fusion, at a red heat, is easy and very liquid, 

 like that of siliceous stones. The mass becomes of a greyish- 

 yellow. M. Vauquelin satisfied himself by means of ignition 

 with chlorate of potash, that the black colour is owing to 

 carbon ; the quantity of which he determined from the volume 

 of resulting carbonic acid. From the smell evolved by the 

 action of potash on the mineral, he infers the presence of a 

 small quantity of ammonia in it ; which seems to be in the 

 state of a muriate. He could not estimate its amount. The 

 presence of sal-ammoniac, charcoal, iron, and sulphur, says 



