292 FOOD AND FOOD ADULTERANTS. 



the estimation of the CO 2 direct j or with a suitable apparatus for the 

 retention of water, thus estimating it by loss or indirectly, its liberation 

 from the beer being accomplished by the aid of heat. But this manner 

 of manipulation gives simply the amount of carbonic acid capable of 

 being held in solution by a liquid of the density and temperature of the 

 beer when it was measured out, supposing it to have been fully charged 

 previously. The excess of gas above the saturation point, however, 

 which is held by the beer so long as it is kept under pressure, or at 

 a low temperature, escapes as soon as the pressure is removed and gives 

 the beer its " head," which is so desirable a qualification. This excess 

 of gas soon passes off, but during this short interval the beer is drank. 

 The problem is to estimate the carbonic acid just as it exists in the beer 

 as it is consumed. This is a difficult matter with beer contained in 

 casks or kegs, though it might be done by drawing the sample off by 

 gas-tight connections as in gas analysis. But where the beer is fur- 

 nished in stoppered bottles it is an easy matter and furnishes a most 

 valuable index as to the freshness and proper preparation of the beer. 

 Where secondary fermentation or souring has set in, there will be an 

 excess of carbonic acid arid the beer will have become cloudy. 



Where there is a good content of carbonic acid, but the acidity of 

 the beer is very low, the indications are that bicarbonate of soda has 

 been added. 



Hassall speaks of the estimation of CO 2 in bottled aerated waters, the 

 gas being drawn off by means of a champagne tap, and Dr. Wiley 1 

 has estimated the CO 2 in koumiss in that way, using a calcium chloride 

 tube for retention of the water carried off by the gas, and estimating it 

 by difference, the whole bottle being weighed. In applying this form of 

 apparatus to beer considerable difficulty was experienced on account of the 

 viscosity of the liquid ; the bubbles formed were so tenacious that when 

 the bottle was connected directly with a calcium chloride or sulphuric 

 acid tube, the latter would become filled with the beer in a very short 

 time. This difficulty was obviated by the use of the form of apparatus 

 shown in the accompanying figure, devised by Mr. T. C. Trescot and 

 myself. 



The cork of the bottle is pierced with a champagne tap, and this is 

 connected with an Erlenmeyer flask, in the broad bottom of which the 

 bubbles are broken and not allowed to pass beyond it ; next comes a 

 U tube filled with sulphuric acid, then a calcium chloride tube, then a 

 soda lime tube to absorb the dried CO 2 . The bottle of beer is placed 

 in a convenient vessel an empty ether can with the tap cut away 

 answers admirably, as shown in the cut which is nearly filled with 

 cold water. After the apparatus is connected the tap is opened slowly 

 and the gas allowed to flow through the apparatus; when it ceases to 

 flow spontaneously a burner is placed under the can and the tcmpcra- 

 1 Ain. Chem. Jour. 1888. Ann. Rept. U. S. Dept. Agr 5 !., 1835, p. 118, 



