SCIENTIFIC SUMMARY. 
425 
Copper ” thus formed, is not a blacMsh-brown mass such as Wiedemann 
obtained, but is bright, lustrous, and bronze-coloured ; it oxidizes very 
quickly in the air, acquiring a beautiful indigo-blue lustre ; when treated 
with dilute nitric acid, it evolves nitric oxide only ; its density is considerably 
less than that of an equal amount of a mixture of copper and oxygen. 
Finally it changes, without loss of weight, into ordinary copper, if preserved 
without access of air, and the change takes place rapidly at 100°. — {Bull. 
Soc. Chim. Paris , 1879, xxxi. 291.) 
The Gray Modification of Tin . — A window in the church of Freiberg, 
which had long been built up, was recently opened, when a wooden box was 
found in a good state of preservation, and enclosing a medal and a number 
of rings. The box may have lain in the niche three or four himdred years. 
The shaking which it underwent during removal from the niche sufficed to 
break the medals and the rings into a great number of pieces, some of which 
came into the possession of Arnulf Schertel, who has published the results 
of an examination of them. — (Jour, prakt. Chern ., 1879, xix. 822.) 
The rings, which are 15 mm. in diameter, and 2 mm. in thickness of 
metal, are, like the medal, cast. The colour is a reddish blue-gray, the 
fracture uneven, but in the case of some fragments distinctly columnar. The 
metal is tin of great purity, free from lead, and containing a trace only of 
iron and sulphur. It is so fragile that it can be broken between the finger 
nails. By merely pouring hot water on the fragments they acquire a brighter 
colour, and a very considerably greater cohesion. Strong pressure, or a 
severe blow brings out a whiter colour. This tin has undergone the molecu- 
lar. change observed by O. L. Erdmann' in organ pipes, composed of tin 
containing some lead, and by J. Fritzsche of St. Petersburg, in blocks of 
Banca tin. The determinations of the specific gravity of the metal made 
with great care gives the numbers 5-809, 5*781, and 5*808 ; fragments were 
next placed in hot water, and left there for some time until they acquired a 
bright colour. The specific gravities then determined were found to be 
7*280 and 7*304. The gray modification increases in density by treatment 
with hot water, and acquires that of melted tin. Specimens of the gray tin 
described by Fritzsche were found to leave a density of 6*020, 6*002, and 8*930, 
but after treatment with boiling water it rose to 7*24 to 7 '27. A specimen of 
the St. Petersburg gray tin was exposed in a glass vessel to the temperature 
of boiling ether, 35°, for one horn* and a half, at the end of which time it 
had acquired a white hue, and the density of 7 ‘23. A quantity of the 
Freiberg gray tin was exposed in the same way for three hours ; its density 
remained 5*77, and its colour showed no change. When acetone was em- 
ployed in place of ether, and the temperature thereby raised to 50°, the 
brighter hue was at once remarked, and after exposure for a short time to 
a temperature of 59°, its specific gravity rose to 7*279. To test the diffe- 
rence in chemical action of the gray and white modifications of tin, the fol- 
lowing experiment was made. Two large fragments of rings were taken, 
and a platinum wire attached to each piece. One was converted into white 
tin, by immersion in boiling water, and then both were attached by means 
of platinum wires to a galvanometer. The gray variety was electronega- 
tive towards the white variety when dipped in dilute potash solution, in 
hydrochloric acid, or sulphuric acid ; electropositive in dilute sulphuric acid. 
