32 PROCEEDINGS OF THE CALIFORNIA 



If the silica found in this analysis be considered to exist in combination 

 with lime, magnesia, and iron, in the proportions to form olivine, it will be nec- 

 essary to deduct 2.12 per cent, from the amount of metallic iron (equal to 2.73 

 per cent, of protoxyd of iron), in order to give the silicate the olivine formula 

 (3 R 0, Si 3 ). Admitting this to be the correct view, the mass analyzed con- 

 tains 10.07 per cent, of olivine, and by the addition of the oxygen of the pro- 

 toxyd of iron the analysis adds up 99.69 instead of 99.08. 



The variable composition of Schreibersite in different specimens of meteoric 

 iron, and the peculiar character of the insoluble residue of this meteorite, to- 

 gether with the small amount of material in my possession, rendered it impractica- 

 ble to determine the exact amount of this substance contained in the specimen. 



The composition of this meteorite corresponds very closely with another 

 meteoric-iron from Tucson, discovered by Mr. Bartlett, and described by Prof. 

 J. Lawrence Smith, in the American Journal of Science, vol. XIX, page 161. 

 Dr. Smith's analysis gives Iron 85.54, Nickel 8.55, Cobalt 0.61, Copper 0.03, 

 Phosphorus 0.12, Chromic-oxyd 0.21, Magnesia 2.04, Silica 3.02, Alumina, 

 trace=100.18. He considers it to correspond to Nickeliferous Iron 93.81, 

 Chrome Iron 0.41, Schreibersite 0.84, Olivine 5.06=100.18. By an evident 

 inadvertence Dr. Smith adds the magnesia and silica together, and gives the 

 sum as olivine ; these substances are obviously not in the proportions to form 

 the silicate 3 R O, Si 3 , and if we consider the silicate to be olivine, we must 

 reckon the excess of silica as combined with protoxyd of iron. To do this, we 

 must deduct 2.78 from the amount of metallic iron (equal to 2.58 protoxyd of 

 iron), necessary to be combined with the silica and magnesia to give the olivine 

 formula. The amount of olivine contained in the Bartlett meteoric-iron will 

 then be 8.64 per cent. Thus the two masses of iron will be seen to agree very 

 nearly in composition, the only trifling difference being, that Dr. Smith has 

 determined quantitatively the small amount of chromium contained in the Bart- 

 lett meteorite, while I have found a little lime and traces of sulphur and chlorine 

 in the specimen you sent to me. The specific gravity I have stated to be 

 7.39 ; this was taken on about 12.5 grammes of the iron, and probably is some- 

 what higher than the portion which I analyzed, as the two surfaces of the larger 

 mass had been rubbed down, and as thus a considerable portion of the exposed 

 silicate would be mechanically removed, it would make the density correspond- 

 ingly higher. 



I regret that I had not more of this interesting meteorite at my command, in 

 order to have determined more definitely and satisfactorily the character of the 

 insoluble residue. I shall be glad to make a further investigation of this point 

 if you will supply me with more material. 



Very respectfully yours, 



GEO. J. BRUSH. 



After reading the above letter, Professor Whitney added some 

 remarks on the form and locality of the meteoric iron analyzed by 

 Professor Brush, stating the circumstances under which it came in 

 possession of the city of San Francisco. 



