300 Scientific Intelligence. 



even a very little below saturation, the yield falls off greatly. 

 High current density at the anode is also essential. When this is 

 only 5 to 2 amperes per square decimeter, the product contains 

 only from 25 to 55 per cent of percarbonate ; while with a density 

 of from 30 to 60 amperes per square decimeter, it may contain as 

 much as 85 to 95 per cent. By allowing the saturated solution of 

 potassium carbonate to flow slowly in at the bottom of the anode 

 compartment of the electrolytic cell, the best results are obtained. 

 The solution which has already undergone electrolysis floats on 

 this, the solid percarbonate remaining suspended in it slowly 

 flows away; and the percarbonate is collected and dried on a 

 porous plate. From 2*2 to 2 4 grams of percarbonate, containing 

 87 to 93 per cent, is obtained per ampere hour. When dry the 

 percarbonate is only slowly decomposed at 100°, its rapid decom- 

 position requiring 200° to 300°. In aqueous solution, it decom- 

 poses slowly at the ordinary temperature, rapidly at 45°. 

 When perfectly dry, it may be preserved almost without 

 change. It is very little soluble in alcohol, but extremely 

 soluble in water. It may be purified by digestion at —5° to 

 — 10° with concentrated potash solution which dissolves the 

 bicarbonate. The remaining solid after washing with alcohol 

 contains 95 to 99 per cent of percarbonate. — Zeitschr. Elektrochem, 

 iii, 137144, 445-448, Oct. 1896, April 1897. G. f. b. 



6. On the Formation of Natural Petroleum and the Spon- 

 taneous Polymerization of Hydrocarbons. — While the hypothesis 

 that natural petroleums have for the most part been produced 

 by the distillation under pressure of animal fats, and hence 

 accounts for their small content of nitrogen, it fails to account for 

 the high molecular mass, boiling point and density of certain of 

 its constituents; it being well known that the product of the arti- 

 ficial distillation of such fats are mainly low boiling light 

 hydrocarbons. Engler now proposes to ascribe this high molec- 

 ular mass, boiling point and density to the gradual polymeriza- 

 tion of the light hydrocarbons first formed, and has obtained con- 

 siderable evidence of such changes. Thus samples of Galician 

 petroleum increased in density by 0*0011 — 0-0015 in about three 

 weeks, while a Javanese petroleum increased by 0*01 in a few 

 days. Distillates from coal tar showed similar results. The 

 fractions obtained by the distillation of fats under pressure were 

 then examined and proved to undergo a similar condensation. In 

 one case the density increased by about 0*002 in a month ; while 

 in five other cases, there was an increase of density in nine years 

 of 0*016. Since the time which has elapsed since the production 

 of petroleum is very great, it appears probable that its present 

 high density may have been acquired in this way. — Per. Perl. 

 Chem. Ges., xxx* 2358-2365, October 1897. g. e. b. 



7. The Sun's Place in Nature ; by Sir Norman Lockyer, 

 K.C.B., F.R.S., etc., 8vo, pp. xvi, 360. London, 1897 (The Macmil- 

 lan Co., Limited). — This book is a summary of the evidence which 

 its industrious author has been for many years collecting as to 



