c szu 
three weighed tubes containing sulphuric acid and pumice- 
stone, the weight of the third tube being shown to remain 
constant; the air then passed through a Liebig’s Bulbs con- 
taining potash, over two tubes containing solid potash ; and, 
lastly, through two tubes containing sulphuric acid and 
pumice-stone, the weight of the second of these remaining 
constant, lhe volumetric analyses were made in globes of 
7-10 litres capacity, with standard solutions of Baryta-water 
and Oxalic acid, exactly according to the method described by 
Pettenkofer. 
Lhe accompanying Table gives the results of 54 separate 
determinations of thecarbonic acid in the open air of Manchester 
and the neighbourhood, made during the autumn and winter 
months ot lb62-6o-04 ; days being especially chosen upon 
which the amount of caibonic acid might be considered 
likely to be the greatest. 
The tirst and most important conclusion to which these 
experiments lead is that the amount of carbonic acid con- 
tained in Manchester town air differs but very slightly (if at 
all) from that contained in the air of the neighbouring 
country. Thus, from experiments Nos. 23 and 24, made at 
Stretfoi d (four miles west of Manchester) with the wind 
blowing towards Manchester, the quantity of carbonic acid 
found on Feb. 3, 1863, was 3-85 volumes in 10,005 volumes 
of air* as mean of two experiments, whereas on the same day 
the quantity found in the centre of Manchester (Owens 
College) was found to be3'90 vols. in 10,000 vols. of air. as a 
mean of two experiments. Nos. 3 1 , 32, and 33, made at S tretford 
on Fob. 19th, 1863, a damp day, with wind blowing from 
Manchester, showed a mean of 2*77 vols. of carbonic acid. 
