THE CULTIVATION OF DIATOMS. 



37 



mineralising water, the addition of which will give good results in 

 the culture of siliceous algae in fresh water. The salts of soda 

 and of lime are those for which diatoms have a special liking, and 

 it is the same, though in a less degree, with the salts of potash, 

 while those of ammonia are often injurious. 



To mineralise a liquid suitably you may add, with good effect, 

 to a litre of common water, 40 drops of solution A and from 

 10 to 20 drops of solution B : — 



A. 



Thus if the volume of water is only 50 cms. you must add 20 

 times less of these hquids, about 2 and i drops of each solution. 



On a pinch you may dispense with the mineralisation of the 

 ordinary water, and the reason for this is based on the fact that 

 vegetables, which give food to diatoms, contain for the most part 

 the above-mentioned elements in a state of combination, but 

 experience shows that the decomposition of these vegetables being 

 always very slow, the diatoms have generally an excess of organic 

 material and not enough mineral, which retards their develop- 

 ment. Observers may attempt the growth of diatoms in common 

 water, and may be sure of obtaining growths, often very beautiful, 

 but rather sparse. Besides, they must not forget that the formulae 

 I am giving are capable of great improvement, and that they may 



