oOO Mr. T. Graham on Liquid Diffusion applied to Analysis, 



to exist. It was further observed that, by keeping a solution of 

 this binacetate in a close vessel at the boiling-point of water for 

 several days, nearly the whole acetic acid came to be liberated, 

 without any precipitation of alumina occurring at the same time. 

 Mr. Crum boiled off the free acetic acid, or the greater part of 

 it, and thus obtained his soluble alumina. The same result may- 

 be arrived at by dialysing a solution of acetate of alumina that 

 has been altered by heat. In three days the acetic acid was 

 reduced on the dialyser to 11 per cent., giving 1 equiv. acetic 

 acid to 8 equivs. alumina; in six days to 7*17 per cent, acid; in 

 thirteen days to 8*8 per cent, acid, or 1 equiv. acid to 33 equivs. 

 alumina. The alumina exists in an allotropic condition, being 

 no longer a mordant, and forming, when precipitated, a jelly 

 that is not dissolved by an excess of acid. Metalumina resem- 

 bles alumina in being coagulated by minute proportions of acids, 

 bases, and of most salts. Mr. Crum found the solution of met- 

 alumina to require larger quantities of acetates, nitrates, and 

 chlorides to produce coagulation than of the former substances. 

 The solution of metalumina is tasteless, and entirely neutral to 

 test-paper, according to my own observation. 



Like alumina, the present colloid has therefore a fluid and a 

 pectous form — the liquid soluble metalumina, and the gelatinous 

 insoluble metalumina. 



Soluble Peroxide of Iron. — A solution of hydrated peroxide of 

 iron may be obtained by a process exactly analogous to that for 

 soluble alumina. Perehloride of iron in solution is first saturated 

 with hydrated peroxide of iron, added by small quantities at a 

 time; or carbonate of ammonia maybe added in a gradual man- 

 ner to perehloride of iron, so long as the precipitated oxide con- 

 tinues to be redissolved on stirring. These red solutions of iron 

 have lately been carefully investigated by Mr. Ordway (Silliman's 

 Journal, 3 ser. vol. xxxix. p. 197), by M. Bechamp [Annales de 

 Chimie, 3 ser. vol. lvii. p. 293), and by M. Scheurer-Kestner 

 (ib. vol. lv. p. 330). It is observed that the act of solution of 

 the hydrated peroxide by the chloride of iron is a gradual process, 

 demanding time. The quantity of oxide taken up will go on 

 increasing for a long time, if digestion in the cold is continued. 

 Mr. Ordway found chloride of iron to take up so much as 18 

 equivalents of peroxide of iron in the course of five months. 

 This slowness of action is highly characteristic of colloids. 

 Only monobasic acids, such as hydrochloric and nitric, serve for 

 preparing such solutions, — sulphuric and other polybasic acids 

 giving insoluble subsalts with excess of ferric oxide, or of any 

 other aluminous oxide. The red liquid so obtained is already a 

 colloidal hydrochlorate of peroxide of iron, but requires to be 

 dialysed for a sufficient time. Such a compound possesses an 



