246 



The highest value of the tensile strength obtained for glass threads 

 was 3,652 kilograms per square centimeter, while the maximum for gela- 

 tine threads was 3,305 kilograms per square centimeter. It is evident that 

 these values cannot represent the true values or the relative values of the 

 tenacity of glass and gelatine. It may be that the internal strains set up 

 in the gelatine threads were such that the tensile strengths as determined 

 in this experiment were always too low. Or it may be that the "skin 

 effect" in glass threads gave values far beyond the tenacity of glass in a 

 plate. Further experiments along this line are in progress. 



The strength of the gelatine threads was found to increase for a few 

 hours after drawing, and then to decrease — especially when the thread was 

 exposed for a day or 

 two to a dry atmos- 4*00 

 phere. Impurities tend- 

 ed to weaken the 

 threads, Curve A of 

 Fig. 2 showing the ten- 

 sile strength of threads 

 of ordinary glue, Curve 

 B those of gelatine con- 

 taining six per cent of 

 potassium chlorate, and 

 Curve C those of sup- 

 posedly pure gelatine. 

 Gelatine containing six 

 per cent of potassium 

 alum gave a curve sim- 

 ilar to Curve B ; that 

 is, the tensile strength 

 of the gelatine was di- 

 minished by the salt. SCf.cni 

 Still it must be greater 

 than the tenacity of the 

 glass, for in chipping 

 glass about six per cent 

 of some easily crystal- 



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