1822.] Scientific Intelligence. 77 
massive, micaceous iron ore, of great beauty ; actynolite, rose quartz» 
red oxide of titanium, sulphate of strontia, sulphatefof lead, &c. as well 
as of several minerals of importance to the arts, as oxide of man- 
ganese, white granular marble, plumbago, and hematites, 
IX. New Test for Arsenic. 
Dr. Cooper, president of Columbia College, finds a solution ot 
chromate of potash to be one of the best tests of arsenic. One drop is 
turned green by the fourth of a grain of arsenic, by two or three 
drops of Fowler’s mineral solution, or any other arsenite of potash. 
The arsenious acid takes oxygen from the chromic which is converted 
into green oxide. To exhibit the effect, take, he says, five watch 
glasses; put on one, two, or three drops ofa (watery) solution of white 
arsenic; on the second, as much arsenite of potash; on the third, one 
fourth of a grain of white arsenic in the substance ; on the fourth two 
or three drops of solution of corrosive sublimate either in water or 
alcohol; in the fifth, two or three drops of a solution of copper. Add 
to each three or four drops of solution of chromate of potash. In half 
an hour, a bright, clear grass-green colour will appear in numbers 1, 2, 
3, unchangeable by ammonia; number 4 will instantly exhibit an 
orange precipitate: number 5, a green, which a drop of ammonia will 
instantly change to blue. Dr. Cooper, however, does not recommend 
that this test should be exclusively relied on, but merely that it should 
be used in conjunction with others, of which the most unequivocal is 
certainly the actual exhibition of arsenic ina metallic form. 
(Silliman’s Journal.) 
X. Conversion of Cannon Balls into Plumbago. 
In July, 1779, a British squadron from New York invaded the coast. 
of Connecticut ; and, in ontee to favour the movements of a military 
force which had landed, kept up a cannonade in the town and redoubts 
of Newhaven. During a violent storm in September, 1821, part of a 
~ low bank near that town was undermined by the sea, and a cannon ball 
discovered which must have lain undisturbed 42 years. The ground 
in question, where the ball lay, is little else than a salt morass, so that 
it must have been constantly kept moist by sea water. Its diameter 
is 3-87 inches. By means ofa common saw, a section was easily made 
through the plumbaginous coat, which, at the place of incision, was 
half an inch deep, but varied in thickness in different places. The 
plumbago is cut with the same ease, gives the same streak to paper, 
and has in every respect the same properties as common black lead. 
The same article recounts another instance in which a cannon ball, 
covered by oysters, adhering firmly to it, was taken from the wreck 
of a vessel, which appeared to have lain many years under water. 
When the oysters were knocked off, the external part of the ball was 
found converted into plumbago, but the central part remained un- 
altered. It does not, however, appear that this change always hap- 
pened to cast iron when thus exposed; for an old cannon, found 
covered with oysters, did not, in the renewal of its coating, shew any 
signs of such a conversion.*—(Ibid.) 
* In the Annals of Philosophy, vol. v. p- 66, (Jan, 1815) may be found a paper 
by Dr. Henry, on the conversion of cast iron pipes into plumbago. The change seems 
to have been effected by the action of water containing muriate of soda, and muriates 
of lime and magnesia, ; 
