REPORT OF COMMISSIONER OF FISH AND FISHERIES. 33 



are kept has been a subject of experiment since the fall of 1888. Ref- 

 erences to this use of air will be found in the bulletin for 1890 and in 

 the report for 1893. The first object of the experiments was to maintain 

 fishes in salt-water aquaria without circulating the water. Eubber 

 tubing', pricked with pinholes, to liberate air, was tried without satis- 

 factory results. Section of dead grapevine, cornstalk pith, and twigs 

 of various trees were substituted, with little improvement. Sponge, 

 inserted in small openings iu rubber tubes, also gave poor results. 



Finally it was discovered, as detailed in the report for the preceding 

 fiscal year, that twigs of the American linden or basswood furnish per- 

 fect liberators, and the difficult problem was solved. The liberator plugs 

 are made from wilted or dead boughs of any size greater than ^ inch 

 in diameter. The bark is removed and the wood seasoned. It is then 

 cut by a saw with very thin blade and fine teeth into sections ^ inch to 

 £ inch long. The plugs are made from ^ to g inch in diameter by forcing 

 them through a round belt-lacing punch. The ends of the plugs may be 

 smoothed with the finest sandpaper. The liberators continue useful 

 from a few days to several weeks, according to the amount of grit 

 entering the circulation. They were inserted in sections of ^-inch 

 rubber tubing. 



In January, 1891, a Bishop & Babcock air-compressor of large size 

 was introduced to furnish air for the aquaria in Central Station through 

 small iron pipes. It delivers air under pressure of from 5 to 8 pounds 

 per square inch. The water or power cylinder is 1J inches in diameter 

 and 8 J inches long; the air cylinder, 5§ inches by 8.\ inches. Strokes 

 per minute, &yo, delivering 1,105.13 cubic inches of air under a pressure 

 of 7 pounds per square inch, a rate of 301.8 liquid gallons per hour, 

 equivalent to the flow of salt water through the aquaria. At delivery 

 points, 4-iuch brass jet cocks were inserted into the |-inch conduit 

 piping. To the jet cocks were attached sections of i-inch rubber 

 tubing, and air liberators were inserted in the free ends of the tubing. 



The air circulation proved so successful in the aquaria as to lead to 

 the addition of an air pump to the steam plant on car ^No. 3, in August, 

 1893, and the result was equally good. It has been demonstrated that 

 as many fish can be transported in the same bulk of water by air circu- 

 lation as with water circulation. 



In December, 1893, a practical test was made of the practicability of 

 hatching floating eggs by means of air circulation. Cod eggs and sea 

 waiter were obtained from the Gloucester, Mass., Station, and two ship- 

 ments of eggs out of eleven produced fry. 



The eggs were placed in universal hatching jars and the jars were 

 embedded about two-thirds of their height in a mixture of crushed ice 

 and salt, the upper third being free and exposed to a strong light. The 

 water temperature was kept uniformly at 38° F. Air was introduced 

 at the bottom of each jar through a rubber tube provided with a liber- 

 ator. It was believed that the experiment would have been more 

 F. R . 94 3 



