1880.] 



MICROSCOPICAL JOURNAL. 



71 



Batisiied of the fact that they can 

 prove it any time thereafter. In 

 such a case the burning grains may 

 scorch and smut the surface, and 

 the whole grains may bury them- 

 selves entirely below the surface, 

 from beneath which they can readily 

 be dug out, still in a condition 

 capable of exploding. If the grains 

 be small or positive identification 

 be required, by keeping the grain 

 distinctly in view during the 

 manipulation, it should be per- 

 formed only under the microscope. 

 How small a quantity can be thus 

 treated may become an important 

 question. Every intelligent person 

 at all informed as to microscopical 

 manipulation knows that an object 

 of which it would require thousands 

 to weigh a grain, can with perfect 

 ease and certainty be manipulated, 

 examined, preserved and re-exami- 

 ned by any person of ordinary skill 

 and ample experience in such work. 

 To determine whether minute 

 particles of powder could be not 

 only seen and handled but also 

 burned with characteristic results, 

 and finding it inconvenient to weigh 

 such minute quantities, I procured 

 one decigram {j^ grain) of powder 

 carefully weighed, and found it to 

 contain by actual count one-hundred 

 and fifty-three particles. Several 

 of them, of average size, were 

 selected, each of them being by 

 estimate about the 1-lOOth of a 

 grain in weight. One of these 

 particles, tested by being placed on 

 a strip of platinum-foil covered 

 loosely with a cover-glass, and grad- 

 ually heated over a spirit-lamp till 

 it burns, will explode with a dis- 

 tinct flash and an audible sound, 

 both flash and sound being per- 

 ceptible to several persons at once 

 in distant parts of a small room. 

 Similar results, though less in de- 

 gree, were obtained from smaller 

 quantities, estimated to be one- 



tenth as large, or 1-1000 grain. 

 The experiment should be tried in 

 a partially darkened room, but still 

 so light that the black particle can 

 be distinctly seen and its identity 

 assured until it explodes. A cloudy, 

 grayish stain is left upon the under 

 surface of the cover-glass, whose 

 appearance is distinctly shggestive 

 of the flash. As there is usually 

 no difliculty in digging out grains 

 as large as those I have mentioned, 

 this test may be said to be applicable 

 to cases where unaltered powder 

 can be found imbedded. In this 

 manner have been identified as 

 powder, black particles taken from 

 spots which had previously been 

 characterized as pencil-marks, and 

 which, if powder, would absolutely 

 prove a shot to have been fired 

 from a position different from that 

 which was understood to be implied 

 in the theory of the prosecution. 

 Examined under the microscope 

 while still, and recently, imbedded 

 in some dry substance, the powder 

 grains appear to be dry and dark, 

 and granular; and their size may 

 often be so fully determined as to 

 indicate positively to which of two 

 different kinds of powder they 

 belong. After being repeatedly or 

 persistently moistened, they become 

 brownish, and spongy in appear- 

 ance, and may be surrounded by an 

 eftiorescence of nitre which is very 

 characteristic. In some cases they 

 become surrounded by a bluish 

 ring on the white paint they have 

 penetrated, believed to be produced 

 by a reaction between the sulphur 

 of the powder and the lead of the 

 paint. Usually some of the grains 

 only indent the film of paint, or the 

 weather-hardened face of the wood, 

 without imbedding themselves; and 

 this may be true of all if the grains 

 be small, the distance great, or the 

 charge light. At a medium distance, 

 the largest globular grains may 



