Chemistry and Physics. 143 
The barometer is now noted, the temperature of the water sur- 
rounding the receiving-bott tle is observed and the overflowed 
water is weighed, The water contained in the graduated tube 
between its first and second level, must be subtracted from that 
collected in the flask. A sample ‘of commercial zine which gave 
99°80 per cent zinc by Fresenius’s method, gave 99" 39 per cent by 
this. A lot of pepo which gave by this method 80°59 per 
cent of aw yielded 80°10 i ser method of Fresenius. Lape’ rig 
Chem xiii, pets Ma 
Myo Efe —Baytey showed in 1871 8 hag 
the light acai by cilnte paces of cupric salts is deficient 
in those rays which the spectrum of light reflected from ey 
copper has in excess, and hence that if we look at a copper sur- 
face through a sufficient thickness of copper sulphate solution, 
the metal appears silver white, the solution absorbing the exces- 
sive rays which make the copper red. He has now perfected an 
instrument for the ee of copper, founded ees this prin- 
ciple, which he calls ection-cuprimeter. copper mirror 
movable about a aeatatioke axis reflects the direct light of the sky 
settidally upward through ret signe of glass closed at bottom 
by glass plates and having at top convex lenses by which the 
light is concentrated upon two paper ise made translucent by 
acid and diluting to a liter at 15° C. Cov Pee one-half the mir- 
ror with silver, the other half was looked at through a varying 
depth of the nia until both disks were equally white. The 
length of the column requi wa ted, the tubes ears 
graduated for this purpose. In the author’s instrument it wa 
cm. Since the esa of aa column re to shane 
solution, With a solution containing 0°801 gram of copper per 
liter six readings of the oa meter gave °806, 803, 800, 793, 793 
and “813; or ‘803 as am Iron, in the ferrous condition, is not 
injurious, The anberatiog $5 be analyzed, in such quantity as is 
supposed to give a gram of copper, is dissolved in nitric acid, 
