WITH PURE COLLOIDAL SILICA 81 



window an extraordinary number of Torulae were 

 found in fragments of what appeared to have been 

 a layer lining a part of the bottom of the tube 

 (No. 178), a portion of which is shown in Plate 

 10, Fig. 58. In the tube from the north balcony 

 the same kind of Torula? were found, but in much 

 smaller quantity. They were at least twenty times 

 as numerous in the tube that had been at the south 

 window. 



Two days later I charged eighteen of the ordi- 

 nary tubes with a solution in which there were 

 twelve drops of the colloidal silica instead of ten 

 to the ounce of distilled water. Six of these tubes 

 were heated to 125, six to 130, and six to 135 C., 

 each set for five minutes. 



At first there was no appreciable sediment to 

 be seen. All the tubes were placed at the south 

 window, and when examined on the following 

 afternoon, after they had been exposed to bright 

 sunlight all the morning, a very slight flocculent 

 deposit was observed in each, and not appreciably 

 less or more in the tubes that had been heated to 

 125 than in those that had been exposed to 

 135 C. 



All these tubes were opened at periods varying 

 from four to eight weeks, and in every one of 



6 



