154 Chemical Examination of Waters 



cannot be accounted for by a corresponding difference in the 

 amount of phosphate of lime in solution. At the same time it is 

 undoubtedly the fact that the addition of phosphate of lime 

 hinders the action. To a portion of "Woolli Creek water I added 

 some powdered bone earth, and after an hour or two this was 

 filtered and a lead bar immersed. At the end of 24 hours no 

 lead was found in the water. In another experiment a small 

 pinch of bone earth (about 1 gr. to a pint) was stirred up with 

 the water and the lead bar immersed. After 24 hours there was 

 lead found to the extent of about l-10th grain per gallon. The 

 same bar of lead was lightly rinsed and immersed in another por- 

 tion of Woolli Greek water. In 24 hours lead was found to have 

 been dissolved at the rate of about 1 gr. per gallon, showing that 

 no protective coating of phosphate of lead had been deposited in 

 the former experiment. I found also that crystallised common 

 phosphate of soda dissolved in the same water at the rate of 4 

 grs. to the gallon entirely prevented the action of lead. 



Separation of Clay. — Specimens of water taken at different 

 times from the heads of Prospect Creek were always found to 

 be nearly opaque from finely diffused clay ; and this clay separ- 

 ated so slowly that the water was not clear after standing some 

 weeks. Also, when clay from the adopted site of the storage 

 reservoir at Prospect was diffused through Sydney wacer, it was 

 found to be equally lorjg in settling ; while clay from the site of 

 the University, similarly diffused, settled and left the water almost 

 clear in a few days. Filtration through a depth of nine inches 

 of fine sand effected little or no improvement in the water con- 

 taining Prospect clay ; but when alum was dissolved in this water 

 at the rate of two grains to the gallon, separation of the clay 

 began very speedily, and within twenty-four hours the clay had 

 completely subsided, leaving the water clear. A less proportion 

 of alum was not sufficient to clear the water entirely. On com- 

 paring the amount of dissolved solid impurity in the water, before 

 and after the action of alum, it was found that this dissolved 

 matter had increased at the rate of 1" L grain per gallon. The 

 crystallised alum contains 44 per cent, of water, so that it would 

 appear that the alum had left all its solid matter in the water ; 

 but, on the other hand, there may have been double decomposi- 

 tion, and the alumina may have been precipitated, leaving some 

 other base in its place. We find that several other salts have a 

 similar action to alum in removing clay from water, but we have 

 not had leisure to carry the investigation further so as to ascer- 

 tion the kind of action that takes place. 



Tabulae Yiew of the Composition of Waters analysed 

 by Professor Smith for the Commission. 



