CHEMICAL SCIENCE. 207 



xyloid lignite. It is partly soluble in alkali, like the preceding body, 

 but it undergoes a greater alteration, for it dissolves almost entirely 

 in nitric acid and hypoclilorites. 



4. The third state of modification is represented by compact or 

 perfect lignite. Re-agents indicate in this substance a transition 

 from organic matter to coal ; thus, alkaline solutions have generally 

 no effect on perfect lignite ; this combustible is characterized by its 

 complete solubility in hypochlorites and nitric acid. 



5. The fourth degree of modification corresponds to coal, which is 

 insoluble in alkaline solutions and in hypochlorites. 



6. The fifth degree of alteration is anthracite, which is obviously 

 allied to graphite, which resists the re-agents capable of modifying 

 the preceding combustibles, and which is but very feebly attacked by 

 nitric acid. 



It is then evident that chemical reactions confirm the classification 

 of the combustible minerals admitted by geologists. I am, however, 

 far from thinking that lignite, coal, and anthracite, which are now 

 characterized by their elementary composition and chemical reac- 

 tions, constitute the only modifications which organic matters un- 

 dergo while changing into combustible minerals. There doubtless 

 are intermediate transformations of the organic tissues corresponding 

 to the differences established by commercial practice between the 

 different species of coal and lignites. But are the re-agents suffi- 

 ciently sensitive to be capable of characterizing these different va- 

 rieties of the same combustible mineral in glance-coal or smith-coal, 

 or even in the different layers of the same coal-bed ? I shall inves- 

 tigate this question in another communication. Comptes Rendus. 



VALUE OF DIFFERENT KINDS OF SOAP. 



Complaints of consumers in regard to the value, or rather efficacy, 

 of samples of soap, which to the best of the manufacturer's knowl- 

 edge have been well prepared, are not uncommon. It is very proba- 

 ble that the usual explanation which is offered, whenever a soap fails 

 to fulfil the expectations of the consumer, viz., that it contains too 

 much water, may be in many cases correct. Admitting this, and va- 

 rious other contingencies, which are of importance in deciding upon 

 the value of a soap, there appears to be another obvious reason why 

 different soaps containing equal amounts of water may still possess 

 different degrees of efficacy. 



It is evident from the different equivalent weights of the various 

 fatty acids, that the amounts of caustic alkali taken up by them in 

 the formation of soap must be of unlike magnitude. If it be true that 

 the detergent power of soap is entirely dependent upon the amount 

 of alkali which it contains, of course it follows that those soaps which 

 contain the largest proportion of alkali, or, in other words, those con- 

 taining a fatty acid the equivalent weight of which is small, must be 

 the most efficacious. Since the difference between the equivalents 

 of the common fatty acids is not large, these considerations are, per- 

 haps, of little or no importance in so far as concerns the consump- 

 tion of soap in household economy, the total amount used in a single 

 family being but small. In a manufacturing establishment, however, 



