796 



SCIENCE. 



[N. S. Vol. VII. No. 180. 



period of a solar rotation at the equator as 

 determined from the faculse is 24.64 days. 

 The order of rapidity of rotation is faculse, 

 then spots, and last the stratum in which 

 the dark lines are produced which were 

 used by Duner in his spectroscopic determi- 

 nation of the solar rotation. 



The first volume of the Publications of the 

 Zurich Observatory has appeared, aided by 

 a publication fund bequeathed by the late 

 Director, Professor Rudolph Wolf. It con- 

 tains the observations by Professor "Wolfer, 

 now Director, on the solar surface in the 

 years 1887-89. The introduction of photo- 

 graphic methods has not detracted from the 

 value of systematic visual observations of 

 solar phenomena. At Zurich these obser- 

 vations have long been a specialty. Spots, 

 faculse and prominences are included in 

 the observations, which are given in detail 

 with location in heliographic latitude and 

 longitude, followed by charts graphically 

 indicating the distribution. It seems that 

 the faculse in the years 1887-89 had a ten- 

 dency to develop in two special regions of 

 solar longitude nearly diametrically oppo- 

 site to each other. In a less degree this 

 is shown by the spots, and somewhat by the 

 prominences. The Publication is hand- 

 somely printed. 



E. B. F. 



NOTES ON INORGANIC CHEMISTBY. 

 Mangai^^ese salts in which the metal is 

 trivalent are known, but they are few in 

 number, and all are decomposed by contact 

 with water. In the last Journal of the 

 Chemical Society, C. E. Rice describes two 

 double manganic chlorids, MnCIa.SNHjCl. 

 HP and MnCl3.2KCl.H,,0, which are stable 

 up to the temperature of 100°. They are 

 formed by dissolving the higher oxids of 

 manganese in fuming hydrochloric acid, 

 immersed in a freezing mixture and adding 

 a solution of ammonium or potassium 



chlorid. The compounds form minute 

 transparent crystals transmitting ruby-col- 

 ored light. They dissolve in hydrochloric 

 acid to a dark solution, but are decomposed 

 by water. The analogy of manganese to iron 

 is shown by the fact that the crystals are 

 apparently isomorphous with FeCl3.2NH^ 

 Cl.H.O and FeCl3.2KCl.Hp. The chlorid 

 MnCls could not be isolated, and there 

 was no evidence of the formation of any 

 MnCl,. 



The last number of the Chemical Neivs re- 

 prints an article from the Proceedings of the 

 Australasian Association for the Advance- 

 ment of Science, by Professor Liversidge, of 

 the University of Sydney, on the corrosion 

 of aluminum. Two shallow dishes of ordi- 

 nary sheet aluminum 1 mm. thick were 

 exposed on the laboratory roof for over a 

 year. Rain water caught in the dishes so 

 that they were exposed to the action of any 

 dissolved salts of the atmosphere. The 

 metal soon lost its brilliancy, became gray 

 and rough, and the incrustation did not 

 wash off and could not be rubbed off by a 

 cloth. The dishes increased in weight 

 somewhat less than one per cent. The tar- 

 nish was probably due to the formation of 

 a hydrated oxid of aluminum. The tar- 

 nish must be comparatively superficial con- 

 sidering the small increase in weight in 

 over a year's exposure. It is, however, 

 clear that the statement frequentlj^ found 

 in books that aluminum is unaltered by ex- 

 posure to the air is not true of the commer- 

 cial metal, whatever may be the case with 

 the chemically pure metal. In another 

 experiment by Professor Liversidge a sheet 

 of aluminum 1 mm. thick and of 24 square 

 inches' surface was dipped in a solution of 

 salt almost daily for three months, each 

 time being allowed to dry. The plate lost 

 0.1% in weight, and after washing and 

 rubbing dry 0.3%, showing comparatively 



little corrosion. 



J. L. H. 



