stand, the wide tube is put into its right position, and mercury and water are poured into the space between the two tubes, and communication is opened between the inside of the tube _e_ and the mercury between the interior and exterior tubes. This is done by either revolving the interior tube _e_, or by a key turning the nut about the bottom part of _f_. The tube _e_ is filled with gas and water as follows: the tube is removed from the apparatus, filled with mercury, and the gas to be experimented on is passed into it. The volume of the gas is measured, the temperature and pressure determined, and the volume it would occupy at 0° and 760 mm. calculated. A known volume of water is then introduced into the tube. The water must be previously boiled, so as to be quite freed from air in solution. The tube is then closed by screwing it down on to the india-rubber on the nut. It is then fixed on to the stand _f_, mercury and water are poured into the intervening space between it and the exterior tube, which is then screwed up and closed by the cover _p_, and the whole apparatus is left at rest for some time, so that the tube _e_, and the gas in it, may attain the same temperature as that of the surrounding water, which is marked by a thermometer _k_ tied to the tube _e_. The interior tube is then again closed by turning it in the nut, the cover _p_ again shut, and the whole apparatus is shaken in order that the gas in the tube _e_ may entirely saturate the water. After several shakings, the tube _e_ is again opened by turning it in the nut, and the apparatus is left at rest for a certain time; it is then closed and again shaken, and so on until the volume of gas does not diminish after a fresh shaking--that is, until saturation ensues. Observations are then made of the temperature, the height of the mercury in the interior tube, and the level of the water in it, and also of the level of the mercury and water in the exterior tube. All these data are necessary in order to calculate the pressure under which the solution of the gas takes place, and what volume of gas remains undissolved, and also the quantity of water which serves as the solvent. By varying the temperature of the surrounding water, the amount of gas dissolved at various temperatures may be determined. Bunsen, Carius, and many others determined the solution of various gases in water, alcohol, and certain other liquids, by means of this apparatus. If in a determination of this kind it is found that _n_ cubic centimetres of water at a pressure _h_ dissolve _m_ cubic centimetres of a given gas, measured at 0° and 760 mm., when the temperature under which