166 abstracts: engineering 



according as we are dealing'with pressure uniform in all directions (true 

 hydrostatic pressure) or with a mode of compression which does not 

 satisfy this condition, in other words, the effects vary — as indeed is 

 almost obvious — according as the solid retains its original form or under- 

 goes deformation. 



Uniform pressure has a comparatively slight effect on the melting 

 point , it usually raises it, and by an amount, which in the systems hither- 

 to investigated, is seldom greater than 10°, and never greater than 30°, 

 per 1000 atmospheres. Its effect on solubihty is slight, and for practical 

 purposes negligible as compared with the influence of temperature upon 

 solubility. Uniform pressure tends to further those reactions which are 

 accompanied by a decrease of volume; but it by no means follows that 

 it will cause these (or other) reactions to occur, for whether a reaction 

 takes place or not is determined by its velocity under the particular 

 conditions, and such evidence as there is tends to show that reaction 

 velocity is not much affected by uniform pressure. 



The effects of non-uniform pressure greatly outweigh those of uniform 

 pressure. It ahvays lowers the melting-point and raises the solubility, 

 and by amounts which are many times greater than the corresponding 

 changes with uniform pressure. If we make the plausible assumption 

 that permanent deformation of a crystalline aggregate is conditioned by 

 a real local melting (of those parts, which at any moment bear the brunt 

 of the load) , we find the amount of pressure required to cause melting 

 at ordinary temperature to be within the bounds of probability. Such 

 we believe to be the efficient cause in producing most of the phenomena 

 recorded as occurring when solid systems were submitted to compression. 

 This view, while it coordinates satisfactorily the whole of the experimen- 

 tal work hitherto done, conflicts with none of the available direct evi- 

 dence. 



It follows therefore that we can determine the effect of pressure on a 

 solid system only if we can define the character of the compression (with 

 reference to its approach to uniformity or otherwise) as well as its magni- 

 tude, and even then, only when the requisite thermal and other data, 

 characteristic of the system, are available. J. J. and L. H. A. 



ENGINEERING. — The testing and properties of textile materials. 

 Bueau of Standards Circular 41, 1913. 



The scope of textile testing which the Bureau of Standards is now 

 prepared to undertake is summarized below. 



1. Determinations upon raw and unspun fibers: (a) identity of fiber, 



