432 ON THE ARTIFICIAL CULTURE OF MARINE PLANKTON ORGANISMS. 



70° C, at which temperature it should be kept for about twenty 

 minutes. At the same time some animal charcoal is heated sufficiently 

 to sterilize but not to burn it, covered over and allowed to cool. When 

 both are quite cold, the charcoal is added to the water (ca. 15 grm. to 

 1000 cc.) and well shaken up in it several times. After an interval of 

 half an hour or more the water is filtered through fine filter cloth * 

 the whole filter having been first sterilized with boiling sea-water, and 

 is received in a sterile fiask. It is then ready for use. 



2. For many experiments, where larger quantities of water were 

 required, the sea-water was not sterilized before being treated with 

 animal charcoal. In this case, if the first part of the filtrate be 

 rejected, the subsequent water will generally be practically sterile, and 

 few, if any, extraneous organisms will develop in it. 



3. At a later date an automatic apparatus was set up in the 

 Plymouth Laboratory, by which very considerable quantities of sea- 

 water could be treated with animal charcoal, and subsequently filtered 

 through a "Berkefeld" filter; water treated in this manner we call 

 "Berkefeld water." Tank- water was always used in this apparatus, 

 and was mixed with animal charcoal,f in a clean sulphuric acid carboy, 

 by blowing air through with a pair of bellows. The mixture was 

 allowed to settle for at least twenty-four hours and then syphoned 

 over into an inverted bell-jar, with a tubulure at the bottom, into which 

 the Berkefeld candle was fitted. Filtration under these conditions 

 was found to be rather slow ; so, in order to increase its rate, an 

 apparatus was devised by which the pressure on the filter was con- 

 siderably augmented. 



This apparatus (see Fig. 1) consists of a glazed earthenware "tobacco 

 jar " with two tubulures, one at the side, the other at the bottom, and 

 a lid which can be screwed down tightly on to a rubber washer, by 

 means of a triangular metal arrangement fitting into grooves above the 

 lid.J The internal dimensions of our jars are 11x6 inches, and the 

 diameter of the opening at the top is 3| inches. The tubulures are 

 coned, with the smaller diameter external, and make a good fit for 

 a No. 8 rubber bung. When setting up this apparatus, a bung, through 

 which a short glass tube bent at right angles is passed, is fitted into the 



* The iiltei' cloth used for this purpose is the same as is made for use in filter presses, 

 and is known as Extra-Super Swansdown. To prevent tliis becoming clogged another cloth, 

 known as Hydraulic Twill, was, as a rule, used over it. 



t Ca, 300 grm. to 20 litres of water. 



X These jars were made, to our specification, by Messrs. Price, Powell, and Co., Bristol. 

 The clamps usually sui>plied with such jars are not strong enough to obtain a tight joint, 

 but these are easily replaced by stronger ones. 



