PRACTICAL BOOK OF GARDEN ARCHITECTURE 



directions. This is what the experimenters say who 

 speak from actual experience : 



"It is hard for people to believe that the reason 

 for this scum is not frog or fish spawn, nor even the 

 decomposition of the vegetation that grew the year 

 before, and which the winter has killed and the 

 warmth of spring decayed. These misconceptions 

 have existed so long that they have become tradi- 

 tions. This 'purging,' or 'scum/ is alive a micro- 

 organism and exists in hundreds of distinct varie- 

 ties, differentiated and classified by scientists under 

 the general name of algae. The trouble makes its ap- 

 pearance as soon as the weather becomes warm, and 

 often lasts through the entire season. 



"When it is at its height, the fish absolutely re- 

 fuse to take bait, and horses and cattle frequently 

 refuse to drink the water. The method of getting 

 rid of the nuisance is very simple, and consists of 

 applying the copper sulphate in extremely dilute 

 solutions : one part to a million of water. Eoughly 

 speaking, this means five or ten pounds of the sul- 

 phate to each acre of a pond averaging four feet in 

 depth. There is no advantage in using a stronger 

 solution. The exact amount can be computed by 

 ascertaining the number of cubic feet of water in the 

 pond (area multiplied by depth), then by multiply- 

 ing this by 62 J^ (the weight of a cubic foot of water) , 

 and divide by a million. 



58 



