PERMANENT FIREPROOFING OF COTTON GOODS 405 



stannate and the second consisted of sodium tungstate, zinc acetate and 

 sufficient acetic acid to prevent precipitation of the zinc tungstate 

 formed. The result in this case was so good, the material being prac- 

 tically as safe as wool, even after repeated washings, that the first com- 

 mercial permanently fireproofed flannelette which was placed on the 

 market was made on these lines. 



It was soon found, however, that the material thus treated had two 

 serious drawbacks: it had a tendency to go damp, and an unpleasant 

 smell of acetic acid remained, even though the material had been 

 steamed and washed, after the fireproofing process, before being sent 

 out. And apart from these two faults, the fireproofing was still not 

 sufficiently permanent and the cost of the process was too great for it 

 to be considered a satisfactory one. 



A further series of careful comparative tests seemed to indicate 

 that the undoubted advance which had been made was mainly due to 

 the use of the stannate, and it was therefore decided to carry out a 

 series of experiments using salts of tin exclusively. 



The fabric, after being treated with sodium stannate as before, 

 was, in the earlier of these experiments, passed through a fixing bath 

 containing stannous chloride. A very permanent fireproofing was 

 again obtained, but the stannous chloride being a reducing agent, 

 tended to destroy or affect the colors of the material, and the process 

 would, therefore, be generally applicable only to white cloth. 



In order to get over this difficulty stannic chloride was employed, 

 instead of the stannous salt, as the fixing agent, and to avoid any 

 tendering of the material care was taken that the stannic chloride 

 solution should be of such a strength that a little stannate was left 

 unchanged in the material. 



An excellent fireproofing was again obtained, for not only did the 

 material show very little tendency to inflame, after it had been washed 

 several times with soap and water, but it had also in such other respects 

 as appearance and feel almost ideal properties, the only objectionable 

 feature being a slight tendency to dust on rubbing and shaking. Now 

 in this particular experiment, in which sodium stannate and stannic 

 chloride had been employed together, the substance which must have 

 been produced in the fiber, and to which the fireproofing must there- 

 fore have been due, is stannic oxide, and it seemed clear that this oxide 

 or its hydrate must have some remarkable power of combining with, 

 or attaching itself to, the fiber which enables it to resist removal by 

 washing and rubbing. 



But this process still left something to be desired on the score of 

 economy. A certain amount of the tin was undoubtedly wasted, for, 

 in addition to that lost through a portion of the stannate being left 

 unfixed, it was noticed that a considerable amount of the tin oxide 



