( 343 ) 



Afterwards llic solutions rcciuired were always prepared by double 

 decomposition of the pure bariiiin-salt of trichloroacetic acid with 

 ferric sulphate. The pure acid, twice distilled in vacuum (b.p. 94°,8 

 ujider 12 m.m. pressure) was converted by means of barjiumhydroxide 

 into the barium-salt, which crystallises with varying quatjtities of water. 

 A preparation with 25,3 "/o oï ]ja was precipitated with a ferric sulphate 

 of 22,5 "/„ of F(' and the solution was filtered several times in the 

 cold. It has a pale yellow colour and gives no precipitate either 

 with BaCl, or H^SO^ ; it is, moreover, not sensitive (o light, but 

 can be brought in such condition l)y means of an excess of trichloro- 

 acetic acid. 



Another time it was tried to obtain a solution of the salt as 

 concentrated as [)0ssible. A solution of the barium-salt containing 

 4 niols. pro litre, was mixed with a solution of ferric sulphate 

 containing 1.33 mol. pro litre. The BaSO^ now separates in a 

 colloidal, very viscous mass, which prevents a complete decomposition 

 from taking place, even when one of the solutions is poured in a thin 

 stream and with constant stirring into the other. Tiie fdtered liquid 

 is always rich in ii/7-salt, whereas the brownish precipitate, on 

 washing with water, yields a reddish-brown solution, which contains 

 an excess of ferric sulphate. The direct fdtrate is almost colourless 

 and very viscous; after being analysed it is treated cautiously with 

 ferric sulphate until it gives no precipitate with BaCl^ or dilute 

 H^SO^. On repeating the experiment such incomplete decomposition 

 was noticed constantly. 



Although the quantity of the highly concentrated solution thus 

 obtained, amounted only to 200 cm^ many of its properties were 

 studied just because the phenomena observed with these very strong 

 solutions were much more simple than with the diluted ones. A 

 solution containing 32,33 "/u by Aveight of iron salt, corresponding 

 to about 0,06 gram-molecule of salt in 100 grams of solution was 

 especially employed. 



§ 3. Properties of the solution. It has a brownisli-yellow colour 

 but gradually tuins a little darker on exposure to the air; by an 

 excess of water it turns more of a yellowish-brown, and by an excess 

 of trichloroacetic acid it becomes colourless. 



With a little //^ SO^ it becomes nearlj- colourless ; with dilute 

 7/2 SO^ also, but with a very faint tinge of sea-green. 



With a little HNO^ (S.g. 1,4) it turns almost colourless; with an 

 excess, pale yellow. With a little strong //C/ it turns greenish-yellow ; 

 with an excess intensively' orange-yellow. 



