488 abstracts: chemistry 



noted until the sample explodes. In the other form of high temperature 

 test the temperature of the sample is gradually raised until a point is 

 reached at which the sample explodes or at least decomposes with explo- 

 sive violence. 



The decomposition of products of this class is exothermic and auto- 

 catalytic and the temperature of the decomposing material may be 

 few or many degrees removed from the temperature of the heating 

 bath. The amount of this difference will depend on a number of vari- 

 ables, such as the mass of the material, its heat conductivity and the 

 heat conductivity of the systems used for test. These factors enter 

 into the German 135° test as well as into the ordinary high temperature 

 explosion test. In the former, the time will vary with the heat insula- 

 tion, in the latter the explosion temperature will vary with the rate 

 of heating. 



The proposed test consists in the determination of a time temperature 

 explosion curve. The samples are chosen small enough to practically 

 eliminate the factor of heat conductivity of the sample. The apparatus 

 consists of a heating bath which may be kept at various constant tem- 

 peratures. For this work the temperatures chosen were 200°C. ; 180°C. ; 

 170°C; 160°C. The length of time necessary for a sample to explode 

 is determined with the aid of a stop watch at one constant temperature 

 and then at the next and so on. The results are plotted in a curve with 

 time and temperature as ordinates and abscissae. 



That the results are reproducible to within a few per cent is shown 

 by numerous repetitions. After the curve has been plotted by means 

 of three or four points, determinations made at intermediate tempera- 

 tures fall on the curve. The curve is therefore characteristic of the 

 sample. It represents in effect the rate of change of decomposition 

 velocity with change of temperature and as such is an index of the sta- 

 bility of the powder. 



Inspection of the curves show that for stable powders there is a 

 pronounced bend, while the ratio of explosion periods at 200°C. and 

 160°C. is at least 2:9. In the unstable powders this ratio falls as low 

 as 2 : 3 and the irregularities become greater. It also becomes evident 

 that one explosion temperature, even if time is considered, does not 

 give much information. 



It is possible that with sufficient accumulated data the test may 

 throw some light on the actual effect of a stabilizer on the natural decom- 

 position velocity of powders. 



A short resume" of the literature on stability tests is given. 



H. C. P. W. 



