1885.] The Removal of Micro- Organisms from Water. 379 



II. " The Removal of Micro-organisms from Water." By Percy 

 F. Frankland, Ph.D., B.Sc, F.C.S., Assoc. R. Sch. Mines, 

 Demonstrator of Chemistry in the Normal School of Science, 

 South Kensington Museum. Communicated by E. FRANK- 

 LAND, F.R.S. Received May 18, 1885. 



The overwhelming evidence which has been now accumulated of 

 the fact that some at least of the diseases called "zymotic" are pro- 

 pagated by means of living organisms, renders it interesting to dis- 

 cover in what manner snch organisms may be removed from the 

 media — air and water — through which they are in general distributed. 

 In the following pages I have the honour to bring before the Royal 

 Society the results of some experiments upon which I have been 

 recently engaged, with a view to discover whether and to what extent 

 micro-organisms may be removed from water by submitting this- 

 medium to some of the various processes of treatment which are in 

 vogue for its purification. For although the chemical efficiency of 

 numerous methods of water-purification has been largely studied, 

 little has been done in the matter of determining their value as agents 

 for the removal of micro-organisms. 



The method of investigation which I have adopted was to take 

 water in which the number of organisms was approximately known, 

 submit this to treatment in such a manner as not to introduce extra- 

 neous organisms during the experiment, and then determine the 

 number of organisms which remained in a given volume of the water 

 after treatment. Since we are doubtless at present only acquainted 

 with a few of the micro-organisms which are capable of producing 

 disease, it appeared to me to be, in the first instance, desirable to 

 study the question irrespectively of the nature of the organisms, and 

 only to take into consideration their aggregate number before and 

 after treatment. Moreover the employment of specific organisms 

 would in all cases have greatly enhanced the difficulty of the expe- 

 riments, and would in some cases have actually rendered them 

 impossible. 



The organisms generally used in these experiments were those 

 which develope in diluted urine after exposure to the air. The solu- 

 tion was further diluted more or less with water so as to obtain a 

 liquid containing a convenient number of organisms in a given 

 volume. 



The method of determining the number of organisms present in the 

 waters, both before and after treatment, was, with a few modifi- 

 cations, that devised by Koch, in which a definite volume of water is. 

 mixed with sterilised nutritive gelatine and then poured out upon a 



