COLLOID CHEMISTRY. 221 



oxides colloidally dissolved. Precijjitations of albumins by alkali salts, 

 especially in neutral solution, are generally reversible.^ 



The relations of colloid chemistry to technology can here only be 

 briefly alluded to. The industries of indiarubber, gutta-percha, gums, 

 dextrine, glue and gelatine, and cellulose derivatives are of course all 

 colloidal, and it is probable that many reactions which have been 

 described as chemical may really be those of absorption compounds. 

 Tanning and dyeing are particularly concerned with the mutual precipi- 

 tation of colloids and that by inorganic reagents, and in these industries 

 also the distinction between pliysical and chemical reactions in any given 

 case is one of extreme difficulty, which is much accentuated by the want 

 of any method for the separation of colloids comparable with crystallisa- 

 tion, or even fractional distillation. 



Among industries with inorganic colloids may be mentioned the com- 

 paratively new one of the manufacture of colloid fibres for electric glow- 

 lamps from difficultly fusible metals, and both earthenware and agricul- 

 ture are largely dependent on the properties of colloidal suspensions. 

 Glass manufacture is also a colloid industry, and coloured glasses solid 

 colloidal solutions : and modern pigments are largely colloidal precipitates 

 and colour-lakes. 



In conclusion it is only right to acknowledge indebtedness to the 

 excellent work of Dr. Arthur M tiller, ' AUgemeine Chemie der Kolloide,' -^ 

 with its extensive bibliography ; and to the ' Zeitschrift fiir Chemie und 

 Industrie der Kolloide,' edited by Dr. Wolfgang Ostwald, without which 

 the preparation of such a report would have been extremely laborious. 

 Owing to the very numerous and often somewhat inaccessible journals in 

 which important work has appeared, it has been necessary in many cases 

 to trust to abstracts, and it is possible that from this cause full justice 

 has not been done to some authors. 



The Study of Hydro-aromatic Snhstances. — Report of the Committee, 

 consistinij oft)v. E. Divers (Chairman), Professor A. W. Crossley 

 {Secretary), Professor W. H. Perkin, Dr. M. 0. Forster. and 

 Dr. H. E. Le Sueur. 



1 : ^-Dirnethyl-;^--^-dihydroheni:ene and 1 : l-diinethyl-l-'-'^-dihydro- 

 benzene.^ — An account of the preparation of 1 : 1-dimethyl-A-^-dihydro- 

 benzene (II) by the reduction of 3 : 5-dichloro-l : l-dimetLyl-A-=*-dihy- 

 drobenzene (I) with sodium in moist ethereal solution appeared in 1902.^ 



/CH=CCk /CH— CH. 



CileZ Vh -> CMe.,< >Cir. 



\CH.,.CC1'^ ■\CH..CH'^ 



(0 a I) 



Shortly after the publication of this work. Harries and Antoni ^ 

 expressed doubt, not only as to the constitution but also as to the com- 

 position of this hydrocarbon. Their criticisms were, in part, answered 



' The work of Cobnlieim, Chemie der Ebvi'iss]iuri>cr, 1904, aad of Pauli and S.iiio 

 in the Beitr. z. Chem. Plnjs. und Path, from 1903 onwards seems specially wonhy 

 of attention. ^ j ^ Barth, Leipzig, 1907. 



■' Cro.ssley and Renouf, J.C.S., 1908, 93, 629. 



♦ Crossley and Le Rnciir, J.C.S., 1902, 81, S2I. ' Annnlrn, 190.1, 328 SS 



