PROP tant ial g aes toe ek Wee es Nine Sin gote ie nt ae hl 
1896] LABORATORY APPARATUS IN VEGETABLE PHYSIOLOGY 469 
is turned, directing the stream of gas into the other set of tubes. 
During this period the first set of tubes is emptied and refilled 
and made ready for the third period, andso on. The object in 
having the barium solution in long tubes is to bring the gas well 
incontact with the solution, so that any carbon dioxide given off 
by the living material under observation will be taken up and 
precipitated as barium carbonate. The supplementary tube is to 
catch any carbon dioxide that may escape precipitation in the 
the longer tube, usually a very small amount, if any. A definite 
amount of solution is used in each tube, generally 100% in the 
long tube and 20° in the short one, or enough to fill the straight 
portions of the tubes. The two are emptied together at the 
close of the period into a closed vessel, and allowed to stand until 
the precipitate has fallen to the bottom. 
To determine the amount of carbon dioxide that has been 
absorbed by the barium solution during one period, an integral 
part of the solution (20° is a convenient amount), after standing 
until clear, is titrated. A few drops of rosolic acid are added to 
the solution to be tested, as an indicator, and a standard acid 
Solution (1.43188" of dry oxalic acid in 500° distilled water) is 
fun into it from a graduated burette until exactly neutralized, as 
shown by the change of color. The same amount of the origi- 
nal barium solution is similarly titrated. The difference in the 
number of cubic centimeters of the standard solution used for 
each represents the number of milligrams of carbon dioxide 
absorbed by the integral part of the barium solution titrated, for 
one cubic centimeter of the standard acid solution will convert 
a8 much barium into an oxalate as one milligram of carbon diox- 
ide will change to a carbonate. To find the total number of 
milligrams of carbon dioxide given off during the period, mul- 
tiply the difference just obtained by the factor that represents 
the ratio of the full amount of barium solution employed in the 
trial to the amount titrated (six in the case supposed ). 
This apparatus is found to work witha steady water pressure, 
but sudden changes in pressure are very detrimental. Its accu- 
facy is also all that is usually required. 
