534 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



where on the surface. Any number of sheets, from one to six, 

 can be placed one upon the other, after being dampened with 

 the solution, and by interposing these in the circuit, screwing 

 the press down so as to secure a proper contact, and by es- 

 tablishing the circuit, one wire being connected with the up- 

 per bed and the other with the lower, the desired result is ac- 

 complished in a few seconds. 3 A, April 20, 1872, 335. 



DENDRITIC MARKS ON PAPER. 



According to Mr. Liversedge, the minute dendritic marks 

 frequently noticed on paper, to which various observers have 

 assigned a vegetable origin, are actually inorganic ; blow-pipe 

 examinations, supplemented by special tests, showing that they 

 consist mainly of sulphide of copper. These usually have a 

 nucleus, which consists of a minute particle of copper or brass, 

 and probably derived from some part of the machinery used 

 in the manufacture of the paper. 1 A, June 14, 1872, 284. 



ABSORPTION OF METALLIC SALTS BY WOOL. 



A memoir on the absorption of metallic salts by wool when 

 mordanted, submitted by Professor M. P. Havrez, was very 

 favorably received by the Royal Society in Brussels. The ac- 

 tion of the mordants which usually have alum as a basis 

 is not confined to making the coloring principle insoluble 

 and thus fixing it upon the tissue, but also imparts to the tint 

 purity and intensity of color. The Avay of proceeding has 

 always been empirical, as the influence of the many possible 

 modifications has never been fully ascertained. Mr. Havrez, 

 in experimenting with tepid and boiling solutions of alum of 

 different strength, used the salt in eleven different propor- 

 tions, gradually increasing the amount from one twentieth of 

 one per cent, of the quantity of w r ool to 100 per cent. The 

 feeble solutions had an alkaline reaction ; those more impreg- 

 nated were acid. The cause of this difference Mr. Havrez at 

 first attributed to traces of soda retained in the wool, to lime 

 in the water used for washing, and finally to the presence of 

 ammonia, resulting from the alteration of the gelatinous prin- 

 ciple of the wool. Mr. Stas then pointed out, as the true 

 cause, the dissociation of the alum, and the extended experi- 

 ments of Mr. Havrez have confirmed this supposition. Di- 

 luted solutions of sulphate of iron and copper give entirely 



