Letts & Bhaxe—The Carbonic Anhydride of the Atmosphere. 227 
The following are the results :— 
Carsponic ANHYDRIDE AT N. T. P. 
Difference. 
Number. Taken. Found. 
Absolute. Percentage. 
1 1-900 c.ems, 1°89 c.cms. — ‘010 c.cm. — 0°5 per cent. 
2 1-900 ,, 1:91 99 +:010 ,, +075 ,, 
3 INOBY ag Oo Samat — 007 ,, -063 ,, 
4 1-937 ,, OZ — 017 ,, = (03 in 
The results show that the chief source of error lies in the absorption 
of Carbonic Anhydride from the atmosphere (and breath ?) during the 
transfer of the absorbent from the receiver, and its subsequent titration in 
open vessels. 
As regards the relative delicacy of phenol-phthalein and turmeric 
paper as an indicator, I have made the following experiments :—To 
separate portions of neutralized distilled water—50 cubic centimetres— 
T added, drop by drop, weak standard solution of baryta (one cubic 
centimetre of which = 0:1 cubic centimetre of carbonic anhydride), and 
tested the point at which incipient alkalinity was manifest (A) with 
turmeric paper, and (B) with phenol-phthalein. 
RELATIVE Denicacy or INDICATORS. 
Number. | Turmeric. Phenol-phthalein. 
1 8 drops. 1 drop. 
2 99 I 96 
3 @ 9p 1 ,, 
4 C56 1 5 
5 a 9p 1 ; 
6 Wd) 99 es 
Mean, 7 drops. 
These results show that phenol-phthalein is seven times more delicate 
than turmeric paper when used as an indicator. 
In the modification of Pettenkofer’s process, adopted by Professor 
