396 Prof. N. S. Maskelyns on New Cornish Minerals [1865. 



The formula 3 Cu" H' 2 O 2 + Cu" S0 4 + 2H' 2 O requires the following 



numbers * : 



Calculated Average 



percentage. found. 



4 equivalents of copper 12672 = 52-00 52-55 



4 oxygen 32 = 13-13 (calc. 13-268) 



1 sulphuric anhydride 40 = 16-41 16'42 



5 water . . 45 = 18-46 18'317 



243-72 100-00 100-55 



In order to determine the proportions of water on which the blue colour 

 of the Langite depended, and, if possible, to obtain some insight into the 

 nature, or, at least, the number, of the different degrees of the hydration, 

 1-6987 gramme of the crystals, after having been previously powdered and 

 dried in dry blotting-paper, were heated in an air bath. The result was a 

 loss : 



At 100 C. of -02625=1-54 per cent, water 



Between 100 and 120 C. of -03825=2-25 



120 and 140 C. of -03900=2*30 (begins to turn green). 



140 and 180 C. of -0620 =3-650 

 180 and 190 C. of -0692 =4-216 



190 and 220 C. of '096 =5'651 (turns dark olive). 

 250 C. of -1352 =7-959 

 255 C. of -1402 =8-254 

 260 C. of -1472 =8-616 

 290 C. decomposition. 



2 equivs. ofHO = 7'384. 



The passage, then, of Langite, under the influence of heat, into a substance 

 with the formula 3 Cu" H' 2 O 2 +Cu" SO 4 + H' 2 O would take place at a 

 temperature of about 180 C. ; and it would further pass into a substance 

 with the formula of Brochantite, 3 Cu"H' 2 2 + Cu" SO 4 at a temperature 

 of about 23.0 or 240 C. 



A transition, however, so effected would probably be incompatible with a 

 new crystalline structure in the mineral resulting from it, which would be, 

 in fact, a pseudomorph . 



The high temperature requisite for the expulsion of the last three equi- 

 valents of water, which cannot be performed without decomposition, would 

 seem to give colour to the belief that this water is in more intimate associa- 

 tion with the oxide, and forms with it a hydrate. 



It is a fact worthy of remark that I have found one old specimen in 

 which Langite is associated with Connellite. I convinced myself that the 

 mineral was Langite by removing a crystal and measuring it. It gave the 



* I have adopted in this paper the doubled equivalents of all the elements involved in 

 my formula*, except hydrogen. 



