On the Precipitation of Calcium Carbonate. 



15 



great disadvantage is the strong probability that the sudden reduction in 

 pressure, to which the water is exposed as it enters the bulb, would immedi- 

 ately kill any bacteria in the water. The employment of a metal water- 

 bottle seemed undesirable in view of the bactericidal action of metals. 

 In order to settle this point some test experiments were made with various 

 metals to see if a suitable one could be found. 100 c.c. of water from the 

 laboratory tanks at Plymouth, diluted i in 100 with sterile sea-water, was 

 exposed for 6 hours to the action of about 2 square inches of the various 

 metals, with the following results: 



It is thus obvious that none of these metals are suitable for the work, 

 and probably the only metal that could be used would be platinum, which 

 would be prohibitive on account of the expense. 



In order to overcome these difficulties, a water-bottle on a new principle 

 was designed for me by Mr. Matthews. A purely diagrammatic represen- 

 tation of its method of working is shown in figure i . 



The container of the bottle consisted of a strong glass cylinder B, holding 

 about 250 c.c; this was closed at each end by thick rubber washers W, W, 

 through the center of which a short piece of thin-walled rubber tubing 

 passed, the tubing being sealed at the end within the cylinder. The washers 

 were carried by the plates Pi and P^. The cylinder was carried in a 

 skeleton frame, and by sending down two messengers along the sounding 

 wire 5 it could be first opened and then closed at any required depth. The 

 whole apparatus was first sterilized by steaming in a "Koch," and then 

 the cylinder was completely filled with 95 per cent alcohol ; the washers were 

 kept tight on the ends of the cylinder by strong springs (not shown in the 

 diagram) so that no leakage occurred and the various parts of the apparatus 

 were in the position shown in figure l, A. When the apparatus has been 

 lowered to the required depth, the first messenger is sent doAvn, this hitting 

 the lever Li, releasing the connecting rod Ci and allowing the plate P2 and 



