13 
in the case of the water tubes causes less error. At all events, although 
the results tabulated below may be 1.5 to 2 per cent less than the true 
ones, they are relatively correct. It would require too much space 
to give the calculation involved in obtaining each result tabulated 
below, but in order to give an idea of quantities of reagents used and 
method of carrying out the titrations one experiment will be described 
in full. It is one in which the air of the room was passed through 
cyanide solution and through plain water simultaneously. 
(a) A bsorption in cyanide solution . — 
Tube 1 contained about 8 c. c. KCN solution. 
Tube 2 contained about 5 c. c. KCN solution. 
Tube 3 contained about 2 c. c. KCN solution. 
Tube 4 contained about 8 c. c. 2^ AgN0 3 . 
Tube 5 contained about 10 c. c. distilled water. 
Only the total quantity of cyanide need be measured, which, in this 
case, was exactly 15 c. c., distributed about as stated. There should 
not be less than 8 or 9 c. c. of cyanide solution in the first tube, lest 
there be an excess of uncombined formaldehyde in the liquid at the 
end of the absorption. Distilled water was added to the three cyanide 
tubes to make the column of liquid about 1.5 inches high, and to the 
silver nitrate tube to make a column about 1 inch high. The tubes 
were connected and air drawn through them as described above on 
page 12. 
Volume of air drawn from room=10 liters. 
Time required to draw air=l hour, 4 minutes. 
The five tubes were disconnected. 
Seven c. c. of 
n 
To 
AgN0 3 solution 
were introduced into a 250 c. c. flask and 8 or 10 drops of strong 
nitric acid (about 50 per cent). Through a funnel the silver-nitrate 
solution in tube 4 and its connecting tubes were carefully rinsed into 
the flask, followed in like manner by tubes 1,2, and 3. Then the flask 
was filled to the mark with water and the contents thoroughly shaken. 
One hundred c. c. of the clear filtrate were titrated with sulphocyanate 
for excess of silver nitrate. 
100 c. c. required 1.4 c. c. KCNS solution. 
260 c. c. required 3.5 c. c. KCNS solution. 
3.5 c. c. KCNS solutionX 1.021 = 
3. 57 c. c. 21 AgN0 3 sol. = Excess present. 
15.00 c. c. TAgN0 3 sol. = Quantity taken. 
Difference, 11.43 c. c. 2^ AgN0 3 sol. = Quantity combined with KCN. 
15 c. c. KCNS solution X 0.954 = 
14. 31 c. c. 2^AgN0 3 S( T = Quantity that would have been required if formaldehyde 
had not been absorbed. 
