33 
Standard used 1 cc. = 0-1 mgm. copper. 
Solution contained 0*25 mgm. of copper per litre. Details as before. 
Added 0-3 cc. standard. Colour too dark. 
Added 02 cc. „ Colour rather too dark. 
Added 0-1 cc. „ Colour equal to the other. 
Taken. Found. 
No. 6 0-25 mgm. per litre. ... ...0*20 mgm. per litre. 
In this experiment it was very difficult to determine the 
exact point at which the colours were the same, as the 
intensity of coloration produced was very slight. A further 
addition of O05cc. of the standard could hardly he said to 
produce a noticeable change in the depth of colour. 
I think, therefore, that 05 mgm. of copper per litre = 
0-035 grains per gallon is the smallest quantity which can 
be accurately estimated by this process when working with 
50 cc. of the liquid under examination. 
The amount of lead which can be estimated with accuracy 
is less minute than the amount of copper. 
Standard used lee. = 0T mgm. lead. 
Taken. Found. 
No. 7 Q-25 mgm. per litre... no coloration. 
No. 8 0-5 „ „ 0’4 mgm. per litre. 
No. 9 0-75 „ „ 0-6 „ 
No. 10 .DO „ „ DO „ 
1 mgm. of lead per litre = 0 -07 grains per gallon, is, there- 
fore, the smallest quantity which can be accurately estimated 
by this process when working with 50cc. of the liquid under 
examination. 
By the evaporation of 1 litre of water to 50cc., a quantity 
of copper so small as 0-025 mgm. per litre, or of lead equal to 
0-05 mgm. per litre, can be estimated by this process. In 
other words, the process will estimate 1 part of copper in 
2,000,000 parts of water, or 1 part of lead in 1,000,000 
parts of water. 
Secondly, as to the upper limit. 
