AMMONIA-COBALT BASES. 25 



in previous memoirs. The observed forms are the octahedron and first and second 

 prism. P . oo P oo . P oo . The angles in Dana's notation are (see Fig 1) : 



1 : 1 over the base =? 114° 8' ; over the top = 65° 52'. 



1 : 1 over the terminal edge = 101°— 101° 20' (calculated 107° 12'). 

 O : 1 (calculated) = 122° 56'. 

 : 1» (calculated) = 132° 30'. 



1» : li over the base = 95°; over the top = 85°. 

 a = 1.0916. 



The crystals are usually small but extremely well formed; those which are 

 obtained from solutions containing a little chloride of mercury most frequently 

 exhibit the planes of the first and second prism, and are larger than those which 

 separate from pure solutions. From these measurements, it appears that the chlo- 

 ride of Purpureocobalt is isomorphous with the sulphate of Roseocobalt. This iso- 

 morphism is the more remarkable, inasmuch as a precisely similar case occurs with 

 the chloride and sulphate of Luteocobalt, between which there is a similar differ- 

 ence of constitution. Thus we have 



5NH 3 .Co 2 Cl 3 = 5NH 3 .Co 2 3 ,3S0 3 + 5H0 

 6NH 3 .Co 2 Cl 3 =6NH 3 .Co 2 3 ,3S0 3 +5HO. 



From this it appears that in both cases we have the crystallographic equality 



3C1=0 3 ,3S0 3 +5H0. 



The density of the crystals of chloride of Purpureocobalt, as taken in alcohol, is 

 1.802 at 23° C. ; the atomic volume of the chloride is consequently 139.0. 

 The chloride of Purpureocobalt has the formula 



5NH 3 .Co 2 Cl 3 



as appears from the following analyses : 



0.5215 grs. gave 0.3230 grs. of sulphate of cobalt = 23.58 per cent, cobalt. 



0.4962 grs. gave 0.3013 grs. " " = 23. 51 " " 



0.8514 grs. gave 0.5269 grs. " " = 23.55 " 



1.4116 grs. gave 0.8132 grs. " " = 23.55 " 



0.1550 grs. gave 0.4105 grs. water . . . . = 6.04 per cent, hydrogen. 



0.6116 grs. gave 0.3412 grs. " = 6.19 " " 



0.6124 grs. gave 0.3365 grs. " = 6.10 " " 



1.4184 grs. gave 0.1800 grs. " = 6.11 " " 



1.6636 grs. gave 2.8540 grs. chloride of silver = 42.40 per cent, chlorine. 



0.4154 grs. gave 0.8200 grs. " " = 42.49 



0.1966 grs. gave 0.3365 grs. " " = 42.31 " " 



0.4912 grs. gave 0.8553 grs. " " = 42.52 " " 



0.5963 grs. gave 143 c. c. nitrogen at 18° C. and 112 mm .4 (at 18°.4 C.) = 133.19 c. c. at 0° 



and 160 mm = 28.05 per cent, nitrogen. 

 0.5542 grs. gave 134 c. c. nitrogen at 19° C. and 166 mm .56 (at 19°.4 C.) = 123.26 c. c. at 0° 



and 160 mm = 21.93 per cent, nitrogen. 

 0.6036 grs. gave 168.16 c. c. nitrogen at 152 mm .60 and 15° C, h = 93""".5, t = 15°.6 C, = 



135.08 c. c. at 0° and 160 mra = 28.11 per cent, nitrogen. 

 0.5155 grs. gave 160.39 c. c. nitrogen at 111 mm .39 and 15° C, h = 112°"".1, t = 15° C, = 



128.86 c. c. at 0° and 160 mm = 28.12 per cent, nitrogen. 



The nitrogen in these as in all our analyses was moist. 

 4 



