426 



SCIENCE. 



[N. S. Vol. XVI. No. 402. 



saturation. One hundred per cent, satura- 

 tion (weighed wet) is readily eiiected in 

 ten minutes and after the kiln drying the 

 permanent gain in the weight of the wood 

 will be found to be from 5 to 10 per cent., 

 distributed throughout its whole cellular 

 structure and not on the surface or in the 

 exterior layers only. 



Hard woods, in large sizes up to 12 by 

 12 in. have been so treated, and upon being 

 sawed through have been found to have 

 perfect heart saturation. 



With the mechanical side of the fire- 

 proofing treatment thus perfected, let us 

 turn again to the choice of a chemical which 

 shall prove as fire-resistant as possible and 

 impart this quality to the wood. Some of 

 the qualities that such a chemical should 

 possess may be briefly reviewed. 



1. It must not be of a hydroscopic na- 

 ture, because in such case it would destroy 

 paint and keep the surface of the wood in 

 an undesirable moist condition. For this 

 reason the chlorides of calcium, magnesium, 

 and zinc are excluded, although an attempt 

 has been recently made in a German patent 

 to produce for this purpose a basic chloride 

 of calcium which it is claimed is free from 

 this drawback and is recommended for fire- 

 proofing of wood. 



2. It must not be a volatile substance, 

 because in such case it will gradually be 

 liberated from the cells of the wood and 

 show as an efSorescence, besides leaving the 

 wood after a time weaker in its fire resist- 

 ant character. The ammonia salts, notably 

 the sulphate and chloride, will not stand 

 this test at all satisfactorily. In the dry 

 kiln, the liberation of ammoniacal gas be- 

 gins already at 125° F. and the efflorescence 

 is frequently recognizable even when the 

 surface has been varnished if the wood has 

 been exposed to strong sunshine for any 

 length of time. Of course such efflores- 

 cence speedily ruins the appearance of a 

 varnished wood. 



3. The chemical used must not allow of 

 fungus growth, for in such case the wood 

 will decay more rapidly than untreated 

 wood. Here again the ammonia salts, in- 

 cluding the phosphate as well as sulphate, 

 are unsatisfactoiy, as when the conditions 

 of warmth and moisture are favorable the 

 treated wood develops a fungus rapidly and 

 deteriorates in strength. 



4. If possible the chemical should have 

 exactly the opposite character, viz., a dis- 

 tinct preservative effect, so that the life of ^ 

 the treated wood should exceed that of 

 untreated wood. 



5. There should be no noxious gas liber- 

 ated in the heating or carbonizing of the 

 wood. 



6. The chemical used must not be poison- 

 ous in character, so that splinters impreg- 

 nated with it, if by accident run into the 

 flesh or wounding it, shall not endanger life 

 or health. 



7. It should not cause the corrosion or 

 rusting of metal .which in the form of 

 screws or bolts are passed through it. 



8. The cost must be moderate, as its 

 practical utilization will be barred if the 

 materials be such as to make the process 

 an expensive one. 



After a most exhaustive series of experi- 

 ments, extending over several years with a 

 wide range of compounds, Mr. Ferrell, the 

 inventor of the fireproofing method just 

 referred to, has found in sulphate of alum- 

 ina a compound that appears to answer all 

 the requirements as stated. It has the ad- 

 ditional feature of no slight importance in 

 its bearing upon the fireproofing effect, that 

 when strongly heated it leaves an infusible 

 and non-conducting residue to cover and 

 protect the cellular structure throughout 

 the wood. It absolutely prevents the pro- 

 pagation not only of flame throughout the 

 wood but even of a glow because of its non- 

 conducting and unalterable character. 



Sulphate of alumina in concentrated 



