SUPPOSED COBALTIC ACIDi, 305 



a pale yellowifli tinge. The red part was foluble in water, 

 and the yellowifli remained upon % the filter. , This refidue he 

 confidered as the pure oxide of cobalt. The foluble part was 

 evaporated, and by cooling it depofited certain frnall cryftals, 

 which Citizen Brugnatelli inferred to be a combination of the 

 new cobaltic acid with ammonia. The fupernatant liquor 

 alfo poffeffed evident characters of acidity. 



The author obferved, that his acid might be obtained either it is either co- 

 coloured or colourlefs, according to the methods ufed in pro- °" re " or colour- 

 curing it. Evaporations made by fire left a refidue foluble in 

 water, and afforded a cobaltic acid nearly colourlefs, whereas 

 thofe made in the light of the fun always afforded it more or" 

 lefs red. Citizen Brugnatelli being defirous of afcertaining 

 whether his acid was formed during the operation here de- 

 fcribed, or whether it exifted ready formed in zaffre, boiled Zaffre boiled 

 for twenty-four hours fix pounds of this fubflance in eight J il ^ J* ter af- 

 pounds of water. He filtered the liquid while hot and eva- 

 porated it. When it was reduced to half it became turbid ; 

 the evaporation was continued until no more than one third of 

 the fluid remained. It was then taken from the fire and de- 

 pofited a white fubflance, which was collected upon the filter. 

 The fluid which paffed was of a bright yellow colour, with a 

 fenfibly acid tafle ; it acled in all refpecls the fame as the co- 

 baltic acid obtained by the procefs before pointed out. 



The following are among the properties which Citizen Properties ftated 



Brugnatelli confiders as characleriftic. a * characlenftic 



... of this acid* 



1. It precipitates the folution of filver. 



2. It precipitates lime water in a white coagulum infoluble 

 in water, and in an excefs of acid. 



3. It is feparated from its aqueous folution by alcohol. 



4. It precipitates the acetite and muriate of barites. 



I fhall now proceed to defcribe the experiments I have made New experi- 

 on this fubject, and prefent to the Inftitute the confequences ments * 

 which I deduce from the fame. 



Experiment 1 . I formed the ammoniuret of cobalt by leav- Experiment I. 

 ing zaffre in digeftion in the fun's light in ammonia. I was The aromoniu- 

 careful to agitate the mixture which was included in a mat- ret was formed, 

 trafs, and foon obtained a red colour, that after forty-eight 

 hours became a bright red. I obferved in this fluid a cryflal- 

 lization in confiderable abundance, in the form of white bril- 

 liant needles. This cry flail ization was permanent till the fun 



Vol. I.— April, 1802. X had 



