278 Dr. Playfair on the Nitroprussides, 



Altered Nitroprusside of Barium. 



22. When a solution of nitroprusside of barium is boiled, 

 it deposits a brown precipitate containing both iron and 

 barium*. The solution now crystallizes either in pyramidal 

 or in prismatic crystals, that is, in the first state when cry- 

 stallized slowly, in the second when deposited quickly from 

 a hot solution. It is now found that the salt is inconstant in 

 composition, different preparations giving very discordant 

 results. The salt is however peculiarly difficult to dry, having 

 to be kept in the water-bath for days before it ceases to lose 

 weight ; it abstracts water when dried most speedily from the 

 atmosphere. 



It is found that the carbon is increased in a marked degree. 

 The following two specimens were made at different times and 

 analysed. Analyses I. and II. were made on the same speci- 

 men, but crystallized over again for analysis II. No. III. is 

 oh a totally different specimen. 



I. 14.-40 grs. gave 8-62 grs. BaO, SO^and 3-12 grs. Fe^O^. 



II. 15-90 grs. gave 10-17 grs. BaO, SO^ and 3'68 grs. Fe^ O^ 



III. 14-135 grs. gave 8-47 grs. BaO, SO^ and 3-06 grs. Fe^ O^. 



The combustions were made with chromate of lead. 



I. 1 1-735 grs. gave 7*730 grs. CO^ and 1-390 gr. HO. 



II. 10-610 grs. gave 7-145 grs. CO^ and 0-700 gr. HO. 



III. 14.-045 grs. gave 8*800 grs. CO^ and 1-900 gr. HO. 



I. II. III. 



1st Crystallization. 2nd Crystallization. New portion. 

 Irori .... 15-16 16-27 14*76 



Barium . 

 Carbon j 

 Hydrogen 



35-57 37-59 37-85 



17*96 18-34 17-08 



1-31 0-73 1*50 



But a new portion of barytes salt did not give the same 

 result; the portion analysed was in prismatic crystals, and 

 Crystallized twice. 



I. 11*65 grs. gave 6-58 grs. BaO, SO^ and 2*49 grs. Fe^ O^. 

 ll. 17*22 grs. gave 9-83 grs. BaO, SO^ and 3*58 grs. Fe^ O^ 



I. 6-87 grs. gave 3-87 grs. CO^ and 0-52 gr. HO. 

 II. 18-62 grs. gave 7*44 grs. CO^ and 0*69 gr. HO. 



* The barytes used in decomposing the nitroprusside of copper was that 

 made by boiling peroxide of manganese with sulphuret of barium. It 

 always contains a little hyposulphite, and the brown precipitate was found 

 to contain sulphate of barytes. 



