150 



It is a well known f.ict tluit zinc cliloride in solution hyilrolyzes to a 

 considerable extent so that zinc hydroxide or basic zinc chloride precipi- 

 tates, often in larire qnantities. The addition of a stx'oug acid redissolves 

 tlie precipitate, as does also the addition of aluminium sulphate. Tliis 

 soh-ent action of aluminium sulphate is, without doubt, due to the fact 

 that it also hydrolyzes readily in solution, the resulting sulphuric acid 

 thereby acting to repress the hydrolysis of the zinc chloride. Tlie concen- 

 trations of the two salts used in the new process are zinc chloride 39r, 

 aliiiuiniuni sulphate 1.5%. Such a solution is usually clear, so far as any 

 visible precipitate is concerned. Aluminium sulphate is thus seen to be of 

 use in preventing the precipitation and conso(pient loss of zinc chloride in 

 the impregnating solution, but there remains unexplained the reason why 

 two clear solutions, containing the same concentration of zinc, should i>€n- 

 etrate the wood substance to different depths, the solution of the two salts 

 apparently always going farther than the solution of the single salt. It 

 was in order to And, if possible, an explanation of this difference in jiene- 

 trating power, that tlie experiments later described were undc-rtaken. 



The colloidal character of both zinc hydroxide and aluminium hydrox- 

 ide is well known. It seemed likely at the outset that even in clear solu- 

 tions of zinc or aluminium salts there must exist products of hydrolysis in 

 a colloidal condition, consisting of sols of basic salts or even of the hydrox- 

 ides themselves. If this were the case, since the hydrolysis 

 of zinc chloride is repressed by the ])resence of the suli>huric acid 

 formed by the hydrolysis of aluminium sulphate, the clear solution of the 

 composite solution should contain less colloidal and more crystalloidal zinc 

 salt than the single solution. The cellulose composing the wood cells is a 

 vegetable colloid and it is ma i)ossible for other colloids to ditTuse through 

 it. In other words, the wood cells will ad as membranes in carrying on a 

 process of dialysis, retaining colloidal material and allowing crystalloidiU 

 material to pass. If the solutions possess the difference in character as 

 al)ove desciibed it is easy to see that a (lifference in pi'netrating power 

 must follow. The following experiments were undrrtaken to determine 

 wlicthei- zinc chloride solutions in water coiilain more crystalloidal zinc 

 when alnminium sulphate is ))resenl (ban when it is not i>resent. 



EXPEKIMKNTAf.. 



Two sohilions were prepared, each lonfnining (wactly l^'> of zinc chlor- 

 ide. To one of these alnniinum sulphate was added to the anuMUit of 1.5%. 



