Letts & Bhaxe—The Carbonic Anhydride of the Atmosphere. 228 
the laboratory at the time these experiments were conducted), 
was— 
a0 x 1187 = °4748 cubic centimetres of carbonic anhydride. 
In preparing a supply of water for my experiments, this acidity 
was determined and exactly neutralized with baryta. For the standard 
solution, an exactly decinormal hydrochloric acid was first made. 
This was prepared by the use of the corresponding decinormal sodium 
carbonate solution, and then verified, after neutralization, by deci- 
normal silver nitrate solution (which had been factorized by pure 
ammonium chloride), and potassium chromate as indicator. Neutral- 
ized distilled water was used both for the preparation of the sodium 
carbonate solution and also for the preparation of the decinormal 
hydrochloric acid solution, 89:6 cubic centimetres of which, when 
diluted with the same water to 1000 cubic centimetres, correspond with 
100 cubic centimetres of carbonic anhydride at normal temperature 
and pressure. One cubic centimetre of this solution was therefore 
equivalent to 0:1 cubic centimetre of carbonic anhydride at normal 
temperature andi pressure, the strength always employed in the 
determinations. 
The absorbent baryta water was prepared from barium hydrate, 
which had been recrystallized three or four times, and the solution 
was made to correspond with the strength of the acid nearly. Its 
strength was, however, exactly determined in terms of the acid. 
The absorbing vessels used were similar to those employed by Pro- 
fessor Letts and Mr. Blake in their determinations. In the first series 
of experiments, Winchester quart bottles, coated with paraffin wax 
inside, were used, and in the later series of experiments large flasks of 
about six litres capacity and similarly coated, were employed. 
The flasks were filled with the sample of air after the manner 
adopted by Professor Letts and Mr. Blake, namely, by drawing the air 
through them by means of a suction pump, so that the air was 
renewed five times. 
In performing the titrations, the vacuous vessel described in the 
original paper (fig. 4, p. 127) was employed, into which the absorbent 
was drawn from the receiver, together with the subsequent rinsings with 
neutralized distilled water, containing a little phenol-phthalein. The 
burettes were of the special construction, also described in the paper. 
The following are the results of all the different series of experi- 
ments I have made with the two methods. 
I may mention that all the air samples were collected in the 
grounds of the Queen’s College, Belfast. 
