The thermometer used in this research was compared with one which had been recently standardized by the U. S. Bureau of Standards; both thermometers read to 0.1° C.
Ordinary distilled water often retains an acid reaction even after air freed from by passing through tubes containing granulated soda lime has been bubbled through it for 72 hours. Accordingly, Professor George A. Hulett, of Princeton University, very kindly offered to have prepared, under his direction and by his well-known method,* 144 liters of distilled water, which were sealed in 144 clean, steamed flasks of pyrex glasa.t The hydrogen-ion concentration of the contents of each flask was tested separately and found to range from 0.80 to 1.0 X the average being 0.9 X or about 6.045 P.
This water was taken to Tortugas and used in all experiments herein mentioned. It retained a constant hydrogen-ion concentration and apparently no injurious elements were derived from the pyrex glass. In the series of experiments wherein the sea-water was diluted with distilled water of about 6 P., each pyrex glass flask was opened by breaking the narrow neck of the flask and the water was used as soon as possible, the opening in the neck of the flask being sealed in the intervals by a plug of soft paraffin. The distilled water of 6 P. used in diluting the sea-water was not aerated and was thus deficient in oxygen. This, however, makes but little difference, for the commensal plant cells in the tissues of Cassiopea are so active in diffuse daylight that the medusa pulsates at a nearly normal rate even if placed in sea water which had been boiled for an hour to expel its air, then restored to its former volume by air-free distilled water and cooled to normal temperature. Thus in daylight the medusa appears to be able, due to its plant cells, to supply nearly if not quite enough oxygen for its normal metabolism. The presence of free in the surrounding sea-water is, however, very toxic and soon stops pulsation, and in dark ness unreduced accumulates, and thus the rate of movement is considerably slower than in daylight.
In another series of experiments, it was desired to dilute sea-water with distilled water of the same hydrogen-ion concentration as that of the sea-water itself. Accordingly, 50 flasks of Professor Hulett's distilled water were broken and the contents poured into a green-glass carboy which had previously contained Merck's distilled water. Air which had been freed from by drawing it through glass tubes containing granulated soda-lime was then bubbled vigorously through this distilled water for 78 hours, after which the water had a P.
of 8. It was protected from the carbon dioxide of the atmosphere by permitting only air which had passed through soda-lime tubes to enter the carboy, and thus it retained an unchanged alkalinity remaining 8 P. from July 4 to 11 inclusive, during which time 139 dilution experiments were conducted with it; after this its alkalinity began to decline while 26 additional experiments were made. The average for the entire series was 7.93 P. or a hydrogen-ion concentration of 1.17 The fixity of the alkalinity at P,, 8 for so many days was probably due to OH ions derived from the alkaline green glass of the carboy, which may have been counterbalanced by a slight leakage of through the rubber stopper of the carboy. Then, when the volume of the water became reduced, the surface over which solution of glass took place was relatively reduced in comparison with the surface capable of absorbing atmospheric and thus the water finally tended toward acidity. Previous to its being used to hold the distilled water the carboy was cleaned by washing it with solutions of HC1, distilled water, KOH, absolute alcohol, and finally distilled water, tak ing precautions to prevent dust from entering.
The rings cut from the subumbrella of Cassiopea were attached to the kymograph lever by threads of catgut (fig. 15) ; while the rings themselves were each placed in 500 c.c. of solution contained in clean glass jars, covered between times of record-taking to prevent evapora tion and to exclude dust.
Each ring was first placed in 500 c.c. of sea-water and its rate and temperature ascertained. It was then transferred to another glass jar containing 500 c.c. of a freshly made solution composed of 475 c.c. of sea-water and 25 c.c. of distilled water. At the end of an hour its rate was again ascertained on the kymograph and it was transferred to another glass vessel which contained 90 per cent sea-water plus 10 per cent distilled water, and thus it was tested in more and more dilute solutions down to 50 per cent sea-water plus 50 per cent distilled water, after which it was replaced in natural sea-water. Rings which have been in 50 per cent sea-water recover more than 80 per cent of their normal rate within an hour after being replaced in pure sea-water, and, if replaced from 70 per cent sea-water, recovery is practically complete at the end of an hour. Even 50 per cent dilution produces, however, little or no permanent injury.