334 Scientific Intelligence. 



tion may possibly merge gradually into that of true solution by 

 carrying the subdivision farther and farther until finally perhaps 

 Ave may have the substance dissociated into ions. Graham sup- 

 posed the non-dialyzability of colloids to be due to the size of 

 their molecules, which were too large to pass through the pores 

 of the membrane. Of the colloidal solutions examined by the 

 authors, ferric hydrate, dissolved in ferric chloride, yielded a 

 fluorescent solution in which no particles could be detected under 

 the microscope, but which showed a dense polarized glow when 

 examined with a beam of light. After being dialyzed, it could 

 not be filtered through a porous cell nor did it diffuse in water. 

 In presence of hydrogen chloride, silicic acid showed no luminous 

 beam and passed readily through a porous cell. A dialyzed por- 

 tion gave a feebly luminous beam. Molybdic acid gave only a 

 very faint track of light. Cellulose dissolved in Schweitzer's 

 solution showed a well marked glow as did also soluble starch. 

 The latter solution did not diffuse. Congo-red in neutral solution 

 gave a well marked polarized luminous beam but did not diffuse 

 nor filter through a porous cell. In alkaline solution it filtered 

 through a porous cell, but showed no luminous beam. Oxyhse- 

 moglobin in water gave a luminous beam perfectly polarized, but 

 did not filter through a porous cell. Magdala-red gave a non- 

 polarized beam and readily filtered through a porous cell. In 

 these experiments we pass from obvious suspension to colloidal 

 solution, from colloidal solution to non-electrolytic crystallizable 

 solution and from these it is probably only one step farther to 

 electrolytic solutions. This change may be regarded as contin- 

 uous. The case however is not one of mere suspension. There 

 must surely be some attraction chemical in its nature, between 

 the molecules of water or of hydrogen sulphide on the one hand 

 and those of mercuric sulphide on the other. So that in every 

 case of so-called very fine suspension there is a certain degree of 

 molecular attraction between the suspended solid and the solvent. 

 The authors therefore consider that they have made out a good 

 primd facie case for the belief that there is a continuous series of 

 grades of solution passing without break from suspension to 

 crystallizable solution. — J. Chem. Soc, lxi, 148, February, 1892. 



G. E. B. 



6. Methods of Gas Analysis. ■ By Dr. W aether Hempel. 

 Translated from the 2d German Edition by L. M. Dennis. 12mo, 

 pp. xvi, 384. London and New York, 1892 (Macmillan & Co.). 

 — Those who have favorably known Dr. Hempel's book in 

 the original will welcome its appearance in English; especially 

 so since the translation has had the benefit of the author's per- 

 sonal revision. It is a standard book on the subject of gas analy- 

 sis and in the new edition, the improved method of air analysis 

 devised by Pettersson is given. There is also a valuable chapter 

 on determining the calorimetrical power of fuel. The translator 

 has presented the author's meaning clearly and accurately. 



G. F. E. 



