324 PHOTOSALTS 



passed through the filter opaque and almost 

 black. I, therefore, put a quantity of the unfil- 

 tered liquid under the receiver of an air pump 

 along with sulphuric acid, and kept it in a good 

 vacuum till the salt became dry. By this pro- 

 cess a portion of the salt at the surface became 

 dark coloured ; but the portion next the bottom 

 of the vessel was in a beautiful fibrous form, and 

 nearly white, at least the shade of green was 

 very slight. The salt, when thus dry, might be 

 left exposed to the air for days without under- 

 going any alteration. Its taste was sweet, astrin- 

 gent, and acid, and it reddened vegetable blues. 

 It dissolved readily in water, and the solution 

 becomes immediately dark coloured. 



To determine its composition I dissolved 

 14'125 grains of it in water, and added to the 

 solution 18 grains of crystallized carbonate of 

 soda. The oxide of iron was all precipitated, 

 the residual liquid contained no iron, and did 

 not alter the colour of vegetable blues. Now, 

 18 grains of crystallized carbonate of soda con- 

 tain 4 grains of soda, which require for satura- 

 tion 6'25 grains of acetic acid, present in 14-125 

 grains of the salt. The iron being collected and 

 peroxided, weighed almost exactly 5 grains, 

 equivalent to 4-5 grains of peroxide of iron. 

 From these experiments the salt was obviously 

 composed of 



