70 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxv. 



The letter here cited was referred by the Assistant Secretary of 

 State to the then Secretar}^ of the Smithsonian Institution, Professor 

 Henr\% who took measures to secure the mass as indicated by the fol- 

 lowing extract from his repl}': 



It would give us great pleasure to subject a portion of the meteorite in question to 

 an investigation in regard to its gaseous contents; and if the gentlemen who own it 

 will present it to the Institution, we will cheerfully pay the expense of transportation. 



Nothing further was heard from the mass until the centennial 3'ear, 

 1876, when the Institution became the possessor by gift of an uncut 

 block of meteoric iron, purporting to be the Casas Grandes mass, 

 exhibited among the Mexican minerals at the exposition, 



DESCRIPTION. 



This is a lenticular mass of iron measuring 97 bv 74 by 46 centi- 

 meters (38 by 29 by 18 inches) and weighing before cutting 1,544.788 

 kilos (3,407 pounds). The outer surface of the mass is almost entirely 

 covered with broad, shallow pittings, some of which, as shown in the 

 plates, are quite large. This outer surface is more or less oxidized and 

 in no way differs from the so-called '' crust surface " of other meteoric 

 irons containing little or no ferrous chloride. 



A portion of the mass was cut for exchange and stud}^ purposes by 

 means of a slotter. The iron machined readily and was no harder 

 than ordinary mild steel, with about the same toughness as a low-grade 

 nickel steel. The surface left by the tool measured 55 and 38 centi- 

 meters in the two longest diameters and was readily worked down with 

 shop files of increasing fineness, and lastly polished with emery flour. 

 The face thus obtained showed a few small scattered nodules and 

 grains of troilite, the largest not over 2 centimeters in diameter and 

 the smaller, and more numerous, not larger than a pin head. No 

 schreibersite, carbonaceous nodules, or stony matter is visible on the 

 polished surface. After exposure to the action of dilute nitric acid, 

 the polished surface develops the beautiful crvstalline structure shown 

 in Plate III. Seen by reflected light, the etched surface shows numer- 

 ous fine lines of a yellowish to tin white color which was found to be 

 schreibersite. The schreibersite is in general lineally arranged and is 

 usually only to be observed b}^ reflected light, though occasionally it 

 is so prominent as to stand in relief, as shown on the face of the cube 

 here figured. 



THE CHEMICAL COMPOSITION. 



The turnings made by the "slotter" were cut into small pieces by 

 means of snips and carefully washed in alcohol and ether to remove 

 any grease or dirt that may have been present, and after thorough 

 drying were bottled and sealed to prevent possible oxidation. A 

 weighed amount (7.02 grams) of these washed clippings was dissolved 



