Aug.,
T H E J O U R N A L OF I N D T J S T R I A L A N D EiVGINEERIA-G C H E M I S T R Y .
1912
The accompanying table gives a few results obtained on mixtures containing various amounts of copper, lead and nickel as noted. These figures are fairly representative of the results which may be obtained by the methods described in the preceding pages.
-Approximate amount.
Method. Regular. . , . , . Regular. . . . Regular. . . . , . Regular. . , , , , hfodified.. . ' Modified.. . . . hfodified.. . . . . Modified.. . . . Modified.. . . . . Modified.. . . . .
Copper. Lead. Nickel, Gram. Gram. Gram.
.. ..
. , . ,
0.03 0.05 25
0 03
.. 0.15 0.08 0 .50
,
.
0.05 0.30 0 66 0.30 0.80 0.80
..
..
.. .. ,
.
' '
0.03 0.05
.. .. ,.
Tin
taken. Gram. 0 4040 0,0568 o,4470 0.1143 0.4O6O 0.1764 0.4272 0,0216 0.1000 0,4530
Tin found. Gram. 0,4038 0.0575 o,4478
Error. Xg,
0.2 0.7 o,8
0.1153
1. o
0.40(j5 0.1763
0.5 0.1 1.1 0.2 0.0 0.4
0.4261
0,0214 0.1000 0.4526
LABORATORY MCCORZIICK WORKS, INTERNATIONAL HARVESTER CO., CHICAGO.
A NEW APPARATUS FOR THE VOLUMETRIC DETERMINATION O F CARBON DIOXIDE. By HOWARDW. BRUBAKER.
Received April 13, 1912
In THISJ O U R S A L for March, 1 9 1 2 , appeared an account, by L. T. Bowser, of a volumetric method for the determination of carbon dioxide. I n this method the carbon dioxide is liberated and then absorbed in a solution of potassium hydroxide. This solution is washed into a I O O cc. graduated flask, water added t o the mark and a n aliquot titrated, using phenolphthalein as the indicator t o the disappearance of the red color, then methyl orange, the second part of the titration indicating the amount of carbon dioxide in the solution. The writer had occasion to try out the method to see whether i t could be used by a class of comparatively inexperienced students of chemistry. As a result of a little experience with the method some objectionable features were found with the apparatus used by Mr. Bowser which make i t impracticable for use by students. Probably the most objectionable feature is the necessity of washing out the potassium hydroxide from the tall absorbing cylinder into a measuring flask. This process requires skilled manipulation, especially since i t is necessary to wash the cylinder thoroughly and yet keep the whole volume of liquid and wash water down to I O O cc., which seems advisable, in order that a sufficiently large fractional portion of the solution may be titrated without using a very large volume. Another objection lies in the fact t h a t a t the end of the decomposition o f the carbonate when n : attempt is made t o distil over some of the liquid, in order t o drive the last portion of carbon dioxide into the absorbing cylinder, there is a tendency for the potassium hydroxide solution to suck back into the condensing apparatus. I n order t o overcome these objections and to make the method applicable for the use of inexperienced students the writer devised the apparatus shown in the accompanying figure. B is a standardized Erlenmeyer flask holding I O O cc. when filled to the mark.
599
C is a I O cc. pipette half filled with glass beads, having a coil of copper wire a t the bottom t o prevent any of the beads from becoming wedged into the tapering part of the tube. Eight cc. of the potassium hydroxide solution (.-5 0 grams KOH in I O O cc. water) are placed in the flask B which is then connected with the condenser as shown in the figure. One gram of the material t o be analyzed is placed in the flask A with about 5 0 cc. of water. The hydrochloric acid is run in from the funnel, drop by drop, until sufficient has been added t o decompose the sample. The carbon dioxide distils into the flask B, forcing the potassium hydroxide solution up into the pipette until i t stands near the top of the broad portion where the bubbles break. There is left a thin layer of potassium hydroxide covering the bottom of the flask. The carbon dioxide which is not absorbed by this layer of potassium hydroxide passes up through the liquid in the pipette and is completely absorbed. After adding the hydrochloric acid the liquid in the distilling flask is heated' and finally boiled for five minutes, the steam condensing and falling into the flask B. As can be seen by the construction of the apparatus, there is no backing up of the potassium hydroxide solution into the condenser even when the flame is entirely removed. This boiling drives the residual carbon dioxide into the absorbing flask where i t is completely absorbed. If there is any doubt
0 cAPPAfF'RTUS
as t o the last portion of carbon dioxide in the flask B having been absorbed, the flask is shaken for a minute or two after disconnecting it and while holding a finger over the opening of the glass tube. After distilling steam over for five minutes the writer
T H E J O U R N A L OF I N D U S T R I A L . A N D E N G I N E E R I S G C H E i V I I S T R Y .
600
has always found the carbon dioxide t o have been completely absorbed. The stopper with the pipette is now partly withdrawn from the flask B, the pipette rinsed out several times into the flask and water added t o the I O O cc. mark. After mixing, a 2 5 cc. portion is taken for titration. The advantages of this apparatus are as follows: I. Ease of construction. 2 . Ease of manipulation. 3. It permits of distilling over as much of the liquid a s desired, t o drive out the residue of carbon dioxide, without experiencing any annoyance due t o sucking back of the potassium hydroxide solution into the condenser. 4. I t eliminates the necessity of transferring the alkaline solution t o another vessel before making it up t o a definite volume, thus also keeping i t away from contact with the carbon dioxide of the air. The following table shows some results obtained with the apparatus here described. SAMPLE. NazC03 NazCOa NazC03 Na~C03 Baking powder Baking powder Baking powder Baking powder Baking powder Baking powder Baking powder Baking powder Baking powder Limestone Limestone Limestone
coz
.
No. 1 No. No. No. No. No. No. No. No.
1 1 1 1 2 2 3 3
FOUSD.
PER CENT.
B y direct titration.. . . . . . . . . . . . . . . . . . . . . B y distillation and titration: 1st r u n . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2nd run., . . . . . . . . . . . . . . . . . . . . . . . . . . . Available C O S , 1st distillation.. . . . . . . . . . . Available C02, 2nd distillation . . . . . . . . . . . Available C o n , 3rd distillation.. . . . . . . . . . . Total C o n , 1st distillation . . . . . . . . . . . . . . . Total Con, 2nd distillation . . . . . . . . . . . . . . . Available Con, 1st distillation . . . . . . . . . . . . Available Con, 2nd distillation . . . . . . . . . . . Available COS, 1st distillation.. . . . . . . . . . . Available Con, 2nd distillation . . . . . . . . . . . Gravimetric method.. . . . . . . . . . . . . . . . . . . . Volumetric, 1st titration Volumetric, 2nd titration. . . . . . . . . . . . . . . .
39.40 39.40 39.45 8.10 8.02 8.10 11 .01 10.91 8 .76 8.62 10.74 10.91 40.25
1
1912
error is in the titration. The end point with phenolphthalein must be approached with care as the disappearance of the red color is rather slow. ITHACA, A-EW YORK.
A MODIFICATION OF THE SWEENEY METHOD FOR CRUDE FIBER. B y CORXELIA KENNEDY. Received May 6, 1912.
The method for the determination of crude fiber as recently modified by M . 0. Sweeney1 does not prove entirely satisfactory for all kinds of feed stuffs, especially those which are rich in protein. I n his method an ether extracted sample of feed is first boiled for 30 minutes with 1.2 j per cent. sulphuric acid. This acid solution is neutralized with I O per cent. sodium hydroxide and 2 0 0 cc. of a boiling 2 . 6 5 per cent. sodium hydroxide solution added and boiled for 30 minutes. The sample is then filtered, washed, dried, weighed, incinerated and reweighed. The acid dissolves certain nitrogenous bodies, pentosans, gums, etc., and when the alkali solution is added a heavy precipitation of some of these materials is caused. This precipitate is weighed with the crude fiber and consequently materially increases the percentage amount of fiber. The following modification of the Sweeney method does away with this difficulty and gives results which check, within the limits of error, with the official method. As in the above method the prepared sample is first boiled with zoo cc. of a 1.25 per cent. sulphuric Official method.
Sweeney’s method.
_----__
A -
Sweeney’s modified. 7 7
c
40.40
When the method is used for the determination of the available carbon dioxide in baking powders, where it is necessary to decompose the sample with water, frothing occurs during the heating of the solution. This makes i t difficult to distil over enough water t o drive out the last of the carbon dioxide. I n order t o overcome this difficulty, when the distillation was carried as far as was practicable, the distilling flask was filled with water throughthe dropping funnel, thus forcing any carbon dioxide into the absorbing flask. By using a solution of z j-30 per cent. alcohol instead of pure water, for decomposing the baking powder, i t was found possible to prevent excessive frothing.’ One could then clear the flask of the last portion of carbon dioxide by distilling over a little of the liquid and thus do away with the necessity of filling the flask with water. I t is necessary t o determine the carbon dioxide in the potassium hydroxide solution used as the absorbing reagent and to apply the correction in each titration. I n the writer’s experience with the volumetric method for carbon dioxide the greatest source of For this improvement of the method, the writer is indebted t o Prof.
G. W. Cavanaugh of Cornel1 University.
Aug.,
Bran . . . . . . .
12.04 11.49
-
11.56
14.21 14.06
-
0.55 Sucreen 14.33 food . . . . . 13.92 14.12
-
Sugar and flax feed..
Oil meal.
...
Bran.
......
__
0.15
0.27 14.67 14.43
__
0.34
6.90 6.89
7.44 7.44
6.90
15.i5
1.63
-
0.00
7.87 7.86
10.20 10.08
7.87
__
12.33 0.57
14.55 0.43
0.24 7 44
7.12 7.08
0.54
-
~
0.01
-
12.47 12.20
15.92 15 58
0.41
__
14.13 2.37
7.10
0.20
0.04
8.81 8.80
10.14
2.27
8.81
0.03
12 95
0.51
-
0.01
0.12
0.01
11.37 11.11
12.95 12.94
11.81 1 . 7 1 1 1 . 6 9 11.75
__
0.26
11.24 ~
__
0.01
0.12
acid. Neutralization is done away with, by making the alkali solution of such strength that i t both neutralizes the acid and leaves the 400 cc. of 1.25 per cent. sodium hydroxide; zoo cc. of a boiling 3 . 5 2 per cent. sodium hydroxide are therefore added, and the whole boiled 30 minutes. The solution and fiber are then thrown onto a linen filter (which works more rapidly than a gooch because of the nature of the solution) and washed free of alkali. (Suction may be used to 1
U. S.Dept. Agr., Bur. of Chem.. B i d . 137, 157.
