EXPERIMENTS INITIATED IN 1909 43 



were very minute and at times not very nu- 

 merous. 



Then, again, as the different samples of sodium 

 silicate vary in their degree of alkalinity, and as, 

 for the obtaining of positive results, it is desirable 

 to use solutions having a faintly acid or neutral 

 reaction, the best course to pursue is for the ex- 

 perimenter to make solutions with two, three, or 

 four drops of the dilute sodium silicate to the 

 ounce of distilled water, the proportion of the 

 other ingredients remaining always the same (that 

 is, six grains of ammonium phosphate and six 

 drops of dilute phosphoric acid for the colourless 

 solution, and merely eight drops of the liquor ferri 

 pernitratis for the yellow solution). He will then 

 test for acidity or neutrality, boil each of the solu- 

 tions for ten minutes, and, some time after they 

 have cooled, compare their respective amounts of 

 deposit, so as to see which is the best number of 

 drops to use with the particular specimen of sodium 

 silicate, in order to obtain a faintly acid or neutral 

 solution with only a very small amount of deposit. 

 In experiments of this kind we require, in the first 

 instance, only to know whether living organisms 

 are or are not to be found; we do not require to 

 find any large number of them, and if they are 



