INDUSTRIAL A N D ENGINEERING CHEMISTRY
1074
Vol. 15, No. 10
Carbon Dioxide Content of Beverages' A Rapid Method for Determination of Carbon Dioxide in Lightly Carbonated Beverages By Joseph Cannizzaro 113 HUDSON ST., NBw YORK,N. Y.
H E writer has had occasion to estimate the carbon dioxide content of beverages, especially near-beer, and has resorted to gas-volumetric and gravimetric methods such as can be found in standard books of analysis. For the most part these are either long and tedious or require one well versed with the method in order to obtain reliable results. Of the gravimetric methods, that of Crampton and Trescot2 was found to be the simplest and comparatively most compact. A modified form of their apparatus was used to check the results of the writer's rapid method. I n principle their method consists in connecting the bottle of beverage with a standard carbon dioxide absorption apparatus and absorbing the gas in some weighed U-tubes; the difference in weight representing the carbon dioxide. This method is tedious and requires at least an hour for its proper execution, and even then the results obtained are not very reliable. Hence to an analyst who is called only once in a while to perform such an analysis its application is not very satisfactory. Obviously, the results of the gas-volumetric method are not accurate, owing to the fact that the carbon dioxide, usually collected over water, is absorbed by the latter to a considerable extent and thus vitiates the results. The rapid method is based on the same principles as Warder's method3 for the determination of a carbonate in the presence of a bicarbonate. It consists in quickly pipetting a definite volume of the well-cooled beverage and transferring, tip of the pipet under reagent, to a measured volume of standard sodium carbonate. The carbon dioxide reacts: Narc08 H20 COZ = 2NaHCOs The sodium bicarbonate being neutral to phenolphthalein at a fairly low temperature while the sodium carbonate is alkaline, the unused carbonate may be titrated with standard acid to the disappearance of the pink color, if the titrated solution is kept a t about 3" to 4" C. As carbonated beverages contain more or less fixed acid, a correction must be applied for their presence. This is easily determined on a separate portion of the sample by boiling to expel the carbon dioxide, cooling, and titrating with the sodium carbonate solution, using phenolphthalein as the indicator. The volume of sodium carbonate used is subtracted from the total volume used before in order to obtain the volume really used up by the carbon dioxide. If the very cold beverage cannot be opened without manifest loss of gas, as indicated by excessive foaming and spilling over, this method cannot very well be applied. In the experience of the author this is of rare occurrence, especially when dealing with near-beer and other cereal beverages. Specifically, the method found most adaptable for bottled near-beer and similar beverages is as follows: PROCEDURE The beer is first thoroughly cooled by means of cracked ice and salt in a pail of suitable size. While cooling, two burets are filled, one with 0.2 N sodium carbonate and the other with 0.2 N hydrochloric acid, the latter having been standardized against the former. Thirty cubic centimeters
T
+
1 2
8
+
Received June 12, 1923. U. S. Dept. Agr., Bur. Chem., Bull. 107, A m . Chem. J . , 8, No. 1 (1881).
of the sodium carbonate are then measured out in a 600CC. beaker. This and a 25-cc. pipet are placed nearby for rapid availability. When the bottle is cold and is still surrounded by ice, it is carefully and quickly opened, without causing the least agitation to its contents, by means of a common bottle opener. The 25-cc. pipet is then quickly inserted into the bottle and the beverage carefully measured and transferred to the sodium carbonate solution, tip of the pipet below the surface of reagent. The gas is seen to be readily absorbed. The solution is then diluted to about 400 cc. with freshly boiled and cooled distilled water (to about 5" C.). One cubic centimeter of phenolphthalein indicator is then added and slowly titrated with the 0.2 N hydrochloric acid to the disappearance of the pink color. Twice the volume of the hydrochloric acid used is subtracted from the 30 cc. of the sodium carbonate in order to obtain the volume of the latter really used up by the carbon dioxide and fixed acids. It is clear from the reaction NazCOI 4- HC1 NaHC08 4- NaCl
-
that the volume of hydrochloric acid used with phenolphthalein as the indicator is one-half the volume of the sodium carbonate present of the same normality. To determine the fixed acids, another 25-cc. sample is placed in a BOO-cc. beaker, diluted to 100 cc. and brought just to a boil, avoiding prolonged boiling. It is then cooled by placing in the cracked ice and salt bath, diluted to 400 cc. with very cold distilled water, and titrated with 0.2 N sodium carbonate using phenolphthalein as the indicator to the appearance of a pink color. This volume of sodium carbonate used is then subtracted from the total volume used in the first titration in order to obtain the volume of sodium carbonate used for the carbon dioxide. One cubic centimeter 0.2 N sodium carbonate equals 0.0044 gram carbon dioxide. Although it is highly desirable, when opening the cold bottle containing the sample, to draw the sample in the pipet as rapidly as possible, too much suction must not be applied with the lungs, lest the pressure on the surface of the beer in the pipet be so decreased as to cause evolution of gas. The rate of drawing must be reasonably regulated. This must be kept in mind with beverages containing foaming compounds, as these have a special tendency to foam in the pipet. In such cases, provided the beverage is thoroughly cold, the foam may be disregarded and sucked directly into the mouth. After the proper volume of beverage has been drawn, it may be expectorated. Apparently, an error is introduced in the process of transferring the sample from the bottle to the standard solution, but it is very low, well within the limits of negligence. Moreover, this minute error is inherent in every method of determining carbon dioxide in beverages, contained in bottles sealed with the so-called crown corks. Some beverages are highly colored so that a smaller sample or a larger dilution, or both, must be employed in order to observe the end ppint properly. After some practice the analyst can judge the amount of sample to use and the dilution necessary to secure a solution suitable for titration.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
October, 1923
I n ordinary beverages like near-beer the specific gravity may be taken as 1.025, but if the beverage is somewhat thick it is best to determine it and apply correction accordingly. The specific gravity, however, can generally be neglected in the calculation, as the error incurred is quite inappreciable.
Sample 1
The results of this method have been repeatedly checked against those obtained by the Crampton and Trescot method, and the checks are reasonably within the limits of experimental error. The following table shows eight analyses with a comparison of the gravimetric and the rapid methods:
-PER CENT-CARBONDIOXIDGravimetric Rapid Method Method Difference
2
3
0.386
0,385
0.410
0.402
4
0.399 0.300
0.395 0.306
8
0.450 0.376 0.350
0.444 0.366 0.358
5 6 7
RESULTS AND COMPARISON WITH GRAVIMETRIC METHOD
1075
0.420
0.412
0.001 0.008 0.004
0.006
0.008 0.006 0.010 0.008
The f i s t six samples were near-beer and the last two popular brands of soda water. The same method, with slight modifications, is found in the Official Methods of the Association of Official Agricultural Chemists4for determining carbon dioxide in mineral waters. 4
Assoc. Official Agr. Chem., Methods, 1920, p. 28.
Applications of Vapor Pressure Measurements' By H.S. Davis and Mary D. Davis ARTHURD. LITTLE,INC., CAMBRIDQE, MASS.
N PREVIOUS publica-
I
tions* the writers have described a differential vapor pressure apparatus. Further experimentation and the introduction of the device into commercial work have led to improvements in its design along the lines of durability and ease of manipulation.
flask. If any trouble is encountered in breaking off the capillary ends, it may be entirely eliminated by scratching them, before filling, with a file a t the desired points. FILLING THE CONTAINERS-In previous descriptions detailed instructions have been given for filling small containers by alternate heating and cooling or by alternate lowering and raising of the air pressure. However, these methods are open to the following objections:
A convenient vapor pressure apparatus consists of two similar glass flasks connected to a manometer tube and means whereby sealed glass containers full of liquids may be broken inside the flasks. Full details for the manipulation of such a deoice are given. In the recovery of light oils from coke-ooen gas by oil scrubbing, the light oil vapors are to a1certain extent absorbed as a whole. and selectioe absorption plays a smaller part than might be expected. This fact may be partly due to di8erences in the rates of diffusion of the oapors, the lighter ones tending to outstrip the heavier in their race to the absorbent oil. I t is possible io check up the efficiency of a light-oil recovery plant by measuring the total parfial.pressure of the light oils in the gas at various points in the system, and also their tension from the absorbent oil.
APPARATUS The apparatus (Fig. 1) consists of two similar glass flasks, each with a groundglass stopper and a capillary side tube, with stopcocks, connected to a manometer tube. Each flask is provided with a metal device whereby a small, sealed, glass container may be broken inside it. The following improvements are included in the design shown in the figure: MANOMETER TuBE-This was formerly connected to the flask to form one rigid piece. The writers have found, however, that joints of rubber tubing a t the points shown in the figure do much to relieve strain on the apparatus, and also permit manometer tubes of different lengths to be used on the same apparatus. CONTAINERSFOR LIQuIDs-Formerly the liquid whose vapor pressure was being measured was put into small glass bulbs which were attached to movable rods so that when desired the bulb could be broken against the bottom of the flask. The containers now used are made from pieces of thin-walled tubing of 1to 1.5 cm. outside diameter. The tubing is drawn to a capillary a t one end and sealed off 1.5 cm. from the bulb. At the other end it is drawn to a somewhat larger capillary, which is cut off about 2 cm. from the bulb and left open for filling. The metal breaking device has a holder to support the container in a vertical position inside the flask. When it is desired to release the liquid into the flask, the lower part of the breaking device is grasped with the left hand while the upper part is twisted with the right. This movement, acting on a simple contrivance, breaks off bohh the slender ends from the glass container and allows the liquid to flow evenly into the 1 Received February 12, 1923. 1 THIS JOURNAL, 10, 707 (1918); Advisory Council for ScientificTand Industrial Research of Canada, Report 2 (1918),
1-In the case of high-boiling liquids it is necessary to heat them so hot, in order t o obtain a vapor pressure sufficient to drive the air from the bulb, t h a t decomposition may begin. On the other hand, their vapor tensions at ordinary temperatures are so low t h a t filling the bulb by changes of pressure is a slow process. 2-In dealing with a liquid mixture there is a tendency t o fractional distillation of t h e liquid in the bulb. 3-Occasionally a bulb bursts through a too rapid change of pressure. Sometimes the loss of material in this way is a serious matter.
During recent investigations such methods of filling have been completely discarded and instead a capillary pipet, made by pulling out a piece of narrow tubing at one end, has been used. An outside diameter of 0.5 mm. for the capillary will enable ordinary liquids to be drawn with ease through a piece several centimeters long, and the inside diameter of the stem of the container through which it must pass need be very little larger. Such pipets made from glass tubing of 3-mm. inside diameter, and provided with a graduation mark, have been a great convenience for introducing accurate amounts of liquids into small containers of various kinds.3 SEALING THE CONTAINERS-TOseal successfully the open stem of the container, filled with a volatile liquid, it is first heated evenly in a small flame, about 1 cm. from the bulb, and drawn out to a minute capillary. The container is now put aside and allowed to cool completely, after which the capillary 3 A capillary pipet of this kind should be of great use in many physicochemical operations where it is necessary to introduce measured quantities of liquids into small glass containers which are to be sealed up afterwards in the blowpipe. For instance, measurements of vapor density in the Victor Meyer apparatus, of compressibility by certain methods, and of heats of combustion in the Bertholet bomb are made OQ liquids preferably after enclosing them in such containers.
