6G Notices respeclhig Nevs Books 



cess of muriate of barytes by sulphuric acid, 0.G8 gr. of per- 

 oxide of iron, the proportions were exactly the same as the 

 neutral sulphate of protoxide of iron (Fe S^) would have given; 

 for 29.16:9.78 = 2.03:6.809 



The salt formed was equal to 0.74 gr. of proto-sulphuret of 

 iron (Fe S^); but the residue of the pyrites not decomposed, 

 weighed 4,653 gr.; that is to say, six and seven times as much 

 as the effloresced part. 



{b.) To make sure that the undissolved residue did not con- 

 tain any free sulphui", I dissolved some of the loosest of it by 

 means of nitro-muriatic acid, until there was an entire acidifi- 

 cation of the sulphur. There remained a little silex not dis- 

 solved. The solution furnished 0.64 gr. of oxide of iron and 

 3.82 gr. of sulphate of barytes, which perfectly accords with the 

 composition of deuto-sulphuret of iron, that is to say, pyrites. 

 Since therefore the effloresced part was a sulphate, with a prot- 

 oxide for its base which did not contain any excess of acid, and 

 since there were no traces of sulphur being separated during 

 die efflorescence, it is evident that the effloresced part must 

 have been a proto-sulphui'et of iron, Fe S', which has not yet 

 been found in an isolated state in the mineral kingdom *, and 

 that the remainder, which was not liable to effloresce, had been 

 H deuto-sulphuret, Fe S^ 



The efflorescent pyrites cannot therefore be any thing else 

 than particles more or less crystallized of Fe S*, cemented to- 

 gether by particles more or less numerous of Fe S-, which con- 

 vert themselves by little and little, by exposure to the air, into 

 Fe S^; the pyrites loses then its coherence in proportion as the 

 cement of tlie crystallized particles is destroyed. 



The efflorescence does not therefore furnish any clue to the 

 solution of the question as to the difference between the forms 

 of yellow and white pjrites. 



* It will be recollected that the magnetic pyrites which does not effloresce 

 is a chemical combination of Fe S' + 6 Fe S', 



XIII. Notices respecting New Books. 



fecioGRAPHY, or Examples of Shadows, and Rules for their 

 Projection, intended for the Use of Architectural Draughts- 

 men ; by .Joseph Gwilt, Architect. 8vo. 9s. 



Practical Hints on Composition in Painting; illustrated by 

 Examples from the Great Masters of the Italian, Flemish, and 

 Dutch Schools ; by John Burnet. 4to, 125. 



An Encyclopaedia of Gardening; comprising the Theoiy 

 and Practice of Horticulture, Floriculture, Arboriculture, and 



Landscape 



I 



