SCIENTIFIC SUMMARY. 
457 
has a lead-grey colour, and sufficiently compact to admit of its ready separa- 
tion from the grains of eukairite and the powder of berzelianite. I have 
observed no trace of crystallisation in the mineral. In tenacity and hardness 
it resembles chalkosine. Its specific gravity = 6-9. Before the blowpipe 
crookesite fuses easily, forming a lustrous green-black enamel j the flame 
is coloured intensely green. It is insoluble in hydrochloric acid, but nitric 
acid dissolves it readily and completely. 
Analysis showed it to contain 
Copper .... 
45-76 
Thallium .... 
17-25 
Silver .... 
3-71 
Selenium .... 
33-28 
100-00 
Street Bust a Poison. — The chemical analysis of W. Tichborne, of Dublin, 
would* serve to show that street dust, which 
we all take less or more into 
our nostrils, may be the means of propagatin; 
g various epidemic diseases. At 
all events, the following results of analysis show that street-dust contains a 
very large proportion of organic matter : — 
Moist Dust from Grafton Street, Dublin, October 1866. 
Moisture . . . . , 
. . 33-3 
Organic matter . . , 
, . 25-1 
Inorganic matter . . , 
. . 41-6 
100-0 
Street Dust, October 
1866. 
Soluble salts ... 
. . 1-3 per cent. 
Organic matter . . 
. . 25-1 „ 
Soil from a well-made Poad upon which Sea-water had been used. 
Soluble salts . . . 
. . 7*5 per cent. 
Organic matter . . 
. . 21-1 „ 
Here it will be seen that the salts are about f the weight of the total 
organic matters present. — Vide Chemical News, July. 
The Calculus of Chemical Operations . — The important and philosophic views 
which Sir Benjamin Brodie recently expressed on this subject have been 
considered by "Dr. A. Crum Brown. In a paper by the latter, read before the 
British Association at Dundee, the author stated that there were two points 
which might be taken up for examination (1) The idea of a fractional 
relation between chemical substances ; and (2) the manner in which Sir 
B. Brodie had worked this out. He confined his remarks to the second, and 
stated that his conclusion was that while the two s} r stems are equally con- 
sistent, and may both be treated mathematicaly, Sir Benjamin’s was yet, 
notwithstanding its elegance, simplicity, and consistency, to be rejected, on 
the grounds that his fundamental hypothesis is wholly arbitrary, while 
