Septembee 12, 1902.] 



SCIENCE. 



427 



solution is far more efficient than an alum 

 solution; in fact it would seem as if the 

 alkaline sulphate of the alum simply de- 

 tracted from the power of the aluminum 

 sulphate in the matter of making wood fire- 

 resistant. 



I have before referred to the way in 

 which sulphate or phosphate of ammonia 

 act to make wood fire-resistant, viz., by 

 rapidly liberating ammonia gas, which has 

 the effect of checking the flames on the sur- 

 face of the wood. The fiercer the flame 

 which plays against such wood the more 

 rapid the liberation and exhaustion of 

 the protecting vapor. There is no residual 

 protective substance remaining in the wood 

 and the carbonization of the fiber proceeds 

 apace. 



On the other hand, so soon as the sulphate 

 of alumina of the superficial layer of the 

 wood impregnated with this chemical is 

 decomposed by the heat of a flame, a depos- 

 it of almnina is formed, the non-conducting 

 properties of which rnake it a barrier 

 against the propagation of the carbonizing 

 effect and protect the interior in a very no- 

 table degree. An actual experiment, one 

 of a large number which I carried out joint- 

 ly with the inventor, will illustrate this. 

 If a piece of wood be saturated with a solu- 

 tion of sulphate of alumina of 30° B. 

 strength to a depth of not more than three 

 eighth inch from the surface and the point 

 of the inner blue cone of a strong Bunsen 

 flame be made to impinge upon it and kept 

 in such a position, a boring effect takes 

 place while an abundant separation of 

 aliunina will be observed. The average re- 

 sistance of a piece of one-inch white pine 

 so treated to the complete boring result, 

 with final penetration of the flame to the 

 other side, will be over three hours. If a 

 similar piece of one-inch white pine be 

 'heart-saturated' with ten times the quan- 

 tity of sulphate of ammonia and the same 

 Bunsen flame be applied under exactly 



similar conditions, the average resistance 

 to complete penetration will not be over 

 seventy minutes. These results have been 

 obtained repeatedly and in instances the 

 disproportion was much greater. 



Some very interesting observations have 

 been made on the physical changes which 

 the fireproofing material imdergoes on the 

 continued application of heat. As a result 

 of repeated measurements, it is found that 

 the residual aliunina occupies a space from 

 two and a half to three times as great as the 

 dried salt from which it is formed. Hence 

 in forming it apparently expands to fill out 

 the air spaces and intercellular spaces of 

 the wood very fully. This results in the 

 formation of a very compact non-conduct- 

 ing barrier which interposes itself to the 

 action of the flame and protects the layers 

 of woody tissue upon which it is formed. 

 The protection is therefore a real and much 

 more lasting one than that which could 

 come from the liberation of a gas whose ac- 

 tion, from the nature of things, could be 

 evanescent only. 



In working on a large scale, where heavy 

 timbers or boards in the rough are treated, 

 the saturation with the sulphate of alum- 

 ina solution is always carried out until 

 complete 'heart saturation' is attained as 

 the wood has to be sawed, planed, mortised 

 and otherwise worked and cut into and all 

 surfaces that will be exposed later must be 

 fire-resistant to the fullest degree. 



As, irrespective of the large number of 

 both soft and hard woods that, because of 

 their practical value, had to be tested, the 

 same kind of wood will differ greatly in its 

 physical characters, according as it may 

 be heart-wood or sap-wood, and according 

 as it may be young wood or thoroughly ma- 

 tured, a vast number of saturation tests 

 have been made in establishing the effi- 

 ciency of the different methods of working 

 and the value of different solutions. No 

 deduction has been thought to be of value 



