4 o6 TEE POPULAR SCIENCE MONTHLY 



which was formed by the action of the alkali of the stannate on the 

 stannic chloride, was not permanently fixed in the fibers of the material, 

 and was therefore removed during the subsequent washing. Tin is so 

 expensive that, in a process to be commercially successful, this loss must 

 obviously be avoided. 



There are many ways in which stannic oxide may be precipitated 

 from sodium stannate and one of these, commonly used in ordinary 

 analytical chemistry, consists in adding certain soluble salts, such as 

 sodium sulphate or ammonium nitrate to the solution of the stannate, 

 when the whole of the tin is precipitated as oxide or hydrate. In order 

 to find out whether some process of this kind would precipitate this 

 oxide in such a condition that it would remain permanently fixed in 

 the fiber, a number of pieces of flannelette were soaked in sodium stan- 

 nate and, after thoroughly drying, separately passed through various 

 solutions containing sodium or ammonium salts at the ordinary tem- 

 perature and at temperatures up to the boiling point. Although, as 

 was to be expected, the results were not uniformly good, a certain 

 degree of permanent fireproofing was always achieved and consequently 

 the matter was systematically followed up with the result that a 

 process was gradually evolved which yielded material possessing quite 

 remarkable properties. The process is briefly this : 



The flannelette (or other material) is run through a solution of 

 sodium stannate of approximately 45° Tw. in such a manner that it 

 becomes thoroughly impregnated. It is then squeezed to remove the 

 excess of the solution, passed over heated copper drums in order to 

 thoroughly dry it, after which it is run through a solution of am- 

 monium sulphate of about 15° Tw. and again squeezed and dried. 



Apart from the precipitated stannic oxide, the material now con- 

 tains sodium sulphate and this is removed by passage through water; 

 the material is then dried and subjected to the ordinary processes of 

 finishing. A long series of trials, carried out under the most stringent 

 conditions, have conclusively proved that material, subjected to this 

 process is permanently fireproofed. ISTo amount of washing with hot 

 soap and water will remove the fireproofing agent, or in other words, 

 the property of resisting flame lasts so long as the material itself lasts. 

 I will demonstrate this by exhibiting four different specimens : (t) ma- 

 terial as it leaves the process and before washing, (ii) material which 

 has been washed ten times by hand, (Hi) material washed 20 times in a 

 machine in a laundry and (iv) a portion of a garment which has been 

 in actual use for 2 years, washed every week and is, as you see, in rags. 

 This extraordinary property of resisting soap and water seems to me to 

 indicate that the oxide of tin is not present merely as an insoluble pre- 

 cipitate in the cloth but must have entered into some actual combina- 

 tion with the fiber, yielding a compound which is not broken down by 



