REPORT ON THE COMPOSITION OF OCEAN-WATER. 
147 
presenting “ unit-volume,” and the final calculation based on the mean of the results of 
two well-agreeing calibrations. The volumes are counted from the lower end of the 
capillary tube at the head of the measurer, experience proving that the string of mercury 
suspended in the capillary tube after introducing a gas, never descends by itself. 
AVith a really good telescope, the degree of precision attainable in the analysis is 
greater than might have been expected from the shortness of the measurer. The following 
analyses of a number of samples of atmospheric air, which had been collected by Mr. 
Buchanan during the voyage, are quoted here to show what the apparatus is capable of 
under the most favourable conditions. 
[No. 92.] “Air collected on forebridge, noon, October 29, 1875. Lat. 38° 43' S., 
long. 112° 31' AV.” Vol. of air taken = 376 '22 vol. 
After treatment with caustic potash, 37 5 '74. The contraction of 0‘48 vol. = about 0'3 
mm. of our scale, could not be assumed, in the circumstances, to measure the carbonic 
acid with any degree of precision ; it is merely put down to afford an additional datum 
for criticising the work. 
The residue free from carbonic acid was divided into two parts, which were separately 
analysed by explosion with hydrogen. 
Portion I. — Vol. of air taken = 197'51 ; plus hydrogen = 330'97 ; after explosion, 203'58; contraction = 
“ c ’’ = 124 - 39 ; oxygen = ^ = 41 '463 = 20 '99 per cent. 
Portion //.—Vol. = 178'06 ; plus hydrogen, 268'91 ; after explosion, 157'32; c = 1 1 1 59 ; oxygen = f = 
7497 = 20 '89 per cent. 
[No. 194.] “Air from atmosphere, 1 p.m., December 21, 1875, No. 1367.’ Lat. 
37° 5' S., long. 83° 22' AV 
Vol. of sample = 326'51 ; minus C0 2 =: =326'99 ; contraction= — 0’48(=— 0'3 mm.). 
Residue divided as before. 
Portion /. — Vol. of air = 163'83 ; 'plus hydrogen = 258'84 ; after explosion, 15540; c = 10344; oxygen = 
f = 3448 = 21 '05 per cent. 
Portion II.— V ol. of air = 162 '73 ; plus hydrogen, 240'20; after explosion = 137*67 ; c = 102;53 ; oxygen = 
34477 = 21 '00 per cent. 
[No. 192.] “Sample of air, February 18, 1874, 3.30 p.m.” Lat. 64 44' S., long. 
83° 26' E. 
Vol. of sample = 315 - 06 ; minus C0 2 = 314‘98 ; contraction = 0 '08. Residue divided. 
Portion I. — Vol. = 159'08 ; plus hydrogen = 262'26 ; after explosion = 162 '09 ; c= 10047; oxygen = 33'39 
= 20'99 per cent. 
Portion II. — Vol. = 155 '89 ; plus hydrogen = 23841 ; after explosion, 139 86 ; c = 98'25; oxygen = 32 75 
= 21 '01 per cent. 
