PERMANENT FIREPROOFING OF COTTON GOODS 403 



be fireproof. It furthermore seemed reasonable to suppose that, as the 

 salt is insoluble in water, it would remain in the fiber even after sev- 

 eral washings and therefore that permanent fireproofing might be 

 achieved in this manner. 



A piece of flannelette was therefore soaked in sodium tungstate 

 and, after passing through rollers, to remove the excess of the solution, 

 left for a considerable time in a solution of alum. It was then 

 squeezed, dried and was passed through the same process again with 

 the result that the material became almost as fire-resistant as asbestos. 

 When, however, the piece was thoroughly washed with soap and water, 

 it was most disappointing to find that the greater part of the fire- 

 proofing was removed during the first washing and after several wash- 

 ings the material was little better than the original flannelette. 



While this unexpected result was being investigated, it was noticed 

 that aluminum tungstate is soluble in acetic acid and is reprecipitated 

 when the acetic acid is removed by evaporation or by the action of 

 steam and as the precipitate formed seemed granular in appearance, 

 it was thought that this process, if applied to the flannelette, might 

 yield a better result than the process of double decomposition had done. 

 Accordingly, a solution was made up of sodium tungstate, aluminum 

 sulphate and enough acetic acid to dissolve the precipitate, the flan- 

 nelette was thoroughly soaked in this solution, dried and then placed 

 in an ordinary steamer and subjected to the action of steam until the 

 odor of acetic acid could no longer be detected. 



The material was, of course, non-inflammable and when it was 

 washed it was found that this property was distinctly more resistant 

 to soap and water than was the case in the first experiment, but after 

 several vigorous washings almost every trace of the fireproofing had 

 disappeared. These negative results seemed therefore to indicate that 

 aluminum tungstate was not suitable for the purpose of permanent 

 fireproofing. On the other hand, the failure of this salt was possibly 

 due to some peculiarities in its specific properties and was not consid- 

 ered valid evidence that other insoluble tungstates might not combine 

 more completely with the fiber and thus resist removal by washing. 



A careful examination of the tungstates was therefore made and 

 such insoluble salts only selected for experiment which, like aluminum 

 tungstate, are colorless, since it is obvious that a fireproofing agent to 

 be of any use must be capable of application to white cloth without 

 staining it. Several hundred pieces of flannelette were treated under 

 the most varied conditions with all sorts of combinations which it was 

 known would precipitate insoluble tungstates in the fiber, but in no 

 case was a satisfactory result achieved. 



However, a fact was noticed which afterwards proved to be of value, 

 and it was this, that, of all the salts, the tungstates of zinc and tin 



