164 
ON MARKING INKS. 
which are opaque and have a metallic brilliancy. These ful- 
minate when touched, even though covered by the liquid, and 
often break in pieces the vessels in which they are kept." 
The crystals of which Thomson, or rather Berthollet, here 
speaks, are probably the same as those referred to by Messrs. 
Smee andWalker, and are clearly different from the black inso- 
luble powder. 
Turner again says, " When oxide of silver, recently pre- 
cipitated by barytes or lime water, and separated from adhe- 
ring moisture, by bibulous paper, is left in contact for ten or 
twelve hours with a strong solution of ammonia, the greater 
part of it is dissolved ; but a black powder remains which de» 
tonates violently from heat or percussion." 
Brande gives the following form in which the use of am- 
monia is dispensed with : " One hundred grains of fused and 
finely powdered nitrate of silver are added to an ounce of 
warm alcohol, and the mixture stirred in a sufficiently large 
glass basin ; an ounce of fuming nitric acid is then added, and 
presently a violent effervescence ensues, a powder falls ; as 
soon as this appears white, cold water is added, and the pow- 
der is immediately to be collected upon a filter, washed, and 
dried at a temperature of 212°. In collecting and handling 
this powder, the utmost caution is requisite; it. should be 
made in small quantities only, and touched with nothing hard, 
for it has sometimes exploded upon the contact of a glass rod, 
even under water ; the feather of a common quill serves to 
collect it, and it should be kept in a wide-mouthed vessel 
covered by paper, and by no means in a stoppered or even a 
corked phial, as many serious accidents have arisen from its 
sudden and unexpected explosion." 
Mr. Brande also observes, in the article " Ammoniuret of 
Silver," oxide of silver readily dissolves in ammonia, and 
by particular management a fulminating silver composed of 
the oxide with ammonia, may be obtained." He adds that 
" the oxide of silver should be perfectly pure and thoroughly 
edulcorated, and the ammonia quite free from carbonic 
acid." And further, " chloride of silver is very soluble 
