October, '10] HINDS: fumigation box materials 395 



water manometer, which is far more sensitive than the mercury 

 instrument. 



Furthermore, carbon di-sulfid is one of the best chemical solvents 

 known for waxes, varnishes, oils, etc., such as might be commonly- 

 employed in rendering boxes gas-tight for hydrocyanic gas fumigation. 

 Paint, varnish, putty, paraffin, tarred paper, etc., are very soluble in 

 carbon di-sulfid liquid or gas and cannot, therefore, be used as finish- 

 coats where this material is the fumigant. 



One of our first objects was to find some material which was insolu- 

 ble in carbon di-sulfid liquid or vapor. Glycerine proved to be an 

 effective sealing agent between ground glass surfaces, as in stop-cocks, 

 stoppers, or under bell jars, where the pressure produced by the gas 

 would not be sufficient to lift or separate the surfaces. Animal glue 

 appears to be entirely insoluble in di-sulfid and, at first thought, it 

 appeared that this material might be satisfactory for painting over 

 woodwork, sealing joints, cracks, etc., in fumigation boxes. A diffi- 

 culty soon appeared in the case of glue, however, as external coats are 

 likely to crack and peel, thus rendering them practically worthless. 

 Water glass is another material which, when dry, appears to be resis- 

 tant to the di-sulfid vapor. But water glass cracks even worse than 

 does glue when applied to wood surfaces. Cracking may be reduced 

 to a considerable extent by adding about 10 or 15 per cent, of glycerine 

 •to the water glass, but even then it is unsatisfactory. 



As a general rule for fumigation tents to be used with hydrocyanic 

 acid gas, about 8 ounce duck is employed. In most cases, this is not 

 treated with any filling solution to reduce the porosity of the cloth and 

 recent reports of experiments in tent fumigation indicate that leakage 

 is so large a factor that fumigation is unreliable if there be any consider- 

 able wind blowing. Double and triple filled duck can be used and are 

 improvements over the ordinary grade. 



For fumigation boxes with either hydrocyanic acid gas or carbon 

 di-sulfid, the materials most commonly used are probably matched 

 flooring laid double with paper lining between. The paper is usually 

 well overlapped but the edges not tightly sealed together. In fitting 

 doors and movable windows, various grades of felt or of folded cloth 

 are commonly employed for the bearing surfaces. 



In our experiments, most of the tests have been made with various 

 weights and qualities of duck but other materials have been included 

 and some of these have been treated in various ways. Few people 

 have any definite conception of the real difficulty of constructing an 

 absolutely air-tight fumigation box. Most woods are decidedly porous 

 and especially so if they are cross-grained. In an attempt to construct 

 a small air-tight box, in which an aneroid barometer might be placed 



