1885.] 



Studies of Disinfectants by New Methods. 



269 



was ascertained to be equal to 16' 75 per cent, of the anhydrous sul- 

 phate. 



Equal volumes of the saturated solution and of the sewage were 

 mixed together, and drops weighed out and cultivated at the end of 

 one and twenty-four hours respectively. The results of these experi- 

 ments were as follows : — 



~No. of colonies per gram 

 of the sewage 



taken. 



Sewage containing 8*37 per cent, of 



ferrous sulphate acting for 1 hour . . 1,250 



Sewage containing 8*37 per cent, of 



ferrous sulphate acting for 24 hours 572 

 The control 1,490,000 



Ferric Perchloride. — A solution of perchloride of iron was added 

 to sewage in such proportion that the mixtures of sewage and iron 

 represented 16*4, 9*2, and 5*3 per cent, of ferric perchloride ; the three 

 mixtures were placed on one side at the ordinary temperature for 

 twenty-four hours, weighed drops of each were then taken for culti- 

 vation. 



No. of colonies per gram 

 of the sewage 

 taken. 



1. Sewage treated with ferric chloride 



16-4 per cent * 20,856 



2. Sewage treated with ferric chloride 



9-2 per cent 35,294 



3. Sewage treated with ferric chloride 



5"3 per cent 42,444 



Control 1,490,000 



It was noted that the colonies developed comprised all classes 

 of micro-organisms — mucors, aspergilli, bacilli, bacteria, and micro- 

 cocci having all their representatives. 



The proportion of fungi to the other growths was carefully deter- 

 mined with the following results : — No. 1, the number of fungoid 

 growths to the rest was as 1 : 48 ; in No. 2, as 1 : 5 ; in ~No. 3, as 

 1 : 4. 



Zinc Chloride. — In the same sewage which formed the subject of 

 the previous experiments zinc chloride was dissolved, and the solu- 

 tions allowed to act for twenty-four hours. The following table gives 

 the strength of the solutions, and the number of colonies which were 

 enumerated after four days' cultivation. 



