We have already mentioned that water absorbs a greater amount of carbonic acid with increased pressure. It is found by experiment that this amount increases in proportion to the pressure, as follows: At the pressure of one atmosphere (14.7 lbs.) the water will absorb its own volume; at the pressure of two atmospheres, twice its own volume; at three atmospheres, three times its own volume, and soon, until at about 540 lbs. to the square inch, the carbonic acid gas itself becomes a liquid, as was discovered by Faraday in 1823.

Regarding the amount of carbonic acid gas that water will absorb at different temperatures, we submit the following table:

At a temperature of

Volumes of gas.

0° Celsius

(or 32° F.)

water

will absorb,

1.7967

2°C.

(or36°F.)

"

"

1.6481

4°C.

(or 39° F.)

"

"

1.5126

6°C.

(or 43° F.)

"

"

1.3901

8°C.

(or46°F.)

"

"

1.2809

10° C.

(or50°F.)

"

"

1.1847

12° C.

(or54°F.)

"

"

1.1018

14° C.

(or57°F.)

"

"

1.0321

16° 0.

(or 61° F.)

"

"

0.9753

18° C.

(or 64° F.)

"

"

0.9318

20° C.

(or 68° F.)

"

"

0.9014

In the carbonating process there is, however, a limit to the pressure required, and that limit should be such as to combine with the water the largest quantity of carbonic acid consistent with the safety of the bottles and convenience in opening, and at the same time give requisite pungency to render the carbonated liquids pleasant and palatable. It therefore becomes an important question what should be the limit of pressure, not so much the greatest pressure, but the lowest at which good carbonated water could be produced, because, in using a greater amount of pressure than required, it would cause a waste of gas, greater breakage of bottles, and more difficulty in the bottling. A Mr. Sprules, formerly manager of Pitt & Co.'s Soda Water Manufactory in London, England, being desirous of ascertaining the lowest pressure at which good soda water could be made, went into a number of experiments, beginning with a high pressure and gradually lowering, and the result was that at 95 lbs. per square inch he could produce soda water sufficiently impregnated (this he considered the minimum pressure), and consequently there was a great saving in the breakage of bottles and in the consumption of the gas, while at the same time the bottling was rendered much easier. He did not, however, confine himself to the above pressure, but to a medium between the highest and lowest, and decided on 120 lbs. to 130 lbs. per square inch as the constant working pressure for soda water, and 60 lbs. to 70 lbs. for lemonade and other carbonated beverages containing sugar; and it is rather singular, that in Hamilton's Patent, taken out in 1809, he says, "I generally saturate under a pressure of 120 lbs. per square inch, which is somewhat reduced in the liquors being bottled".

The pressure just mentioned (120 lbs.) has now for many years been considered by the majority of makers the standard at which to bottle soda water. Much discussion has, however, arisen lately, tending to prove that even this pressure is needlessly high if proper care is taken in bottling, and especially if machine bottling is resorted to. There is good reason to believe that waters of the very finest quality can be produced at a pressure never exceeding 100 lbs. in the condenser. It is found that the pressure really retained in the bottles is seldom more than from 40 to 50 lbs., even when bottled with a very high pressure in the condenser, and it is evident that the excess of pressure is to a great extent wasted, involving waste of materials in producing the gas thus allowed to escape.

Where a very high pressure, as 180 or 200 lbs., is used in the condenser, the chief apparent result is that considerable inconvenience, if not danger, is caused to the customer in opening the bottle, and much of the contents flies out and is wasted.