Chemical Society. 331 



as I understood, the destruction of the boiler. On the surface which 

 was next to the copper it is coated by dioxide of copper, and the 

 mass appears made up of an aggregation of prismatic crystals, whose 

 axes are perpendicular to the surface on which the incrustation 

 formed : under a microscope these crystals appear to be six-sided 

 prisms. I compared, under a polarizing microscope, portions of the 

 powder of Iceland spar, and of arragonite from Bilin, with the pow- 

 der of the specimen ; the latter agreed very closely in appearance 

 with that of arragonite. 



" Among the powder of the specimen were seen some very acute 

 double six-sided pyramids; these with little doubt are similar to 

 those formed by G. Rose* by evaporating solutions of carbonate of 

 lime at a boiling heat, and described by him as resembling some 

 sapphire crystals. 



" On chemical examination it was evident that the specimen con- 

 sisted chiefly of carbonate of lime ; water, however, dissolved from it 

 a small quantity of sulphate of lime. 



" The following is the result of an analysis made on 10 grains, but 

 which does not pretend to minute accuracy : — i 



Matter insoluble in muriatic acid, silica, with "I , 

 oxides of iron and copper. / 



Sulphate of lime 1*8 



Carbonate of lime 93*7 



Carbonate of magnesia 3*2 



100 



" Deprived of its coating of dioxide of copper, three trials were 

 made of the specific gravity of its powder ; the sulphate of lime being 

 previously washed off with hot water. 



" The two first trials were made by weighing about 80 grains of the 

 powder in a small spherical-stoppered phial (whose contents in di- 

 stilled water at 62° was previously determined), and then when filled 

 up with water, the third trial was made in the manner described by 

 Rose. The specific gravity being thus determined, the powder was 

 in each case dried, and slightly ignited, (by which operation arrago- 

 nite, as is known, is converted into calcareous spar) and the specific 

 gravity again taken. The results were as follows : — 



Spec. Grav. Spec. Grav. 



before ignition. after ignition. 



1st trial 2-842 2'708 



2nd 2-828 2701 



3rd 2-878 2*681 f 



Mean 2-849 2696 



The specific gravity of arragonite crystals from Bilin is 2*946. 

 "The highest specific gravity which Rose obtained of arragonite, 



[• G. Rose's paper, here referred to, on the formation of calc-spar and 

 arragonite, will be found in Phil. Mag., Third Series, vol. xii. p. 465. — Ed.] 

 f The loss by ignition on 438 grains was a -08 grain. 



