MISCELLANEOUS HINTS. 439 



in common use in England, but scarcely known in this country, 

 and on this account deserving of notice in this place. 



The epreuvette, though the most perfect of all small instruments 

 yet invented for the purpose of testing the strength of gunpowder, 

 if not used properly will often give very unsatisfactory results. 

 The construction of the epreuvette should be perfect in all its 

 parts, more particularly in the spring which controls the move- 

 ments of the wheel on which the graduations are marked. The 

 mouth-piece, or rather the piece which closes the muzzle of the 

 epreuvette and is attached to the gra ding-wheel, should fit closely 

 in its place, so as not to allow any space to be seen between the 

 two surfaces when held up to the light. 



One trial is not sufficient to test the momentum of the powder ; 

 it will be better to make several, and then take the average of the 

 whole. The chamber should be nicely cleaned after each fire, 

 provided we wish to obtain a close analysis. 



POWDER PRESERVED FROM MOISTURE. 



Powder should be kept dry and never exposed to a humid atmo- 

 sphere, as it has a great tendency to imbibe moisture and will soon 

 become unfit for service. If by any mishap it should become damp, 

 it can be dried before the fire, or in the sun, on a metal dish ; a coal 

 fire is the proper kind of fire before which to dry it, a wood-fire 

 being rather dangerous, owing to the chance of sparks flying out, as 

 they frequently do, more particularly if the wood be wet or green. 

 We have dried our powder more than once by putting the dish 

 which contained it on top of a brick placed on a stove. 



The fact of the tendency of powder to absorb moisture may be 

 very fairly and satisfactorily demonstrated by accurately weighing 

 a certain proportion of the article, and placing it in a humid situa- 

 tion for a few hours, when it will be found that it has increased 

 very perceptibly in weight, owing to the imbibition of the aqueous 

 particles of the moist air. All circumstances being equal, small- 

 grained powder will necessarily absorb moisture more rapidly than 

 large-grained, for the simple reason that, in a given weight of 



