123 



At 18 /C 9.75 C C deci normal H 01. 



15.6 9.85 



23. 9.70 



22. 9.65 



22. 9.62 



15.5 9.90 



17.5 9.90 



This expressed in gms. of CaO per 100 CO equals, for the 

 strongest solution (9.90) .1386, and for the weakest (9.62), .1347. 

 The average strength would be about (9.75), .1366, all some- 

 what less than one-twentieth normal solutions (containing 

 .1400 CaO per 100 CO.) 



It may be noticed that while in a general way the strength 

 of solution decreases with the degree of heat there is no uni- 

 form variation, a temperature of 23 holding about as much 

 lime in solution as a temperature of 18. The results are, on 

 the whole, very favorable to the use of lime water as a stand- 

 ard for practical work. 



Lime water has several advantages for use as a standard 

 solution if it can be prepared practically: 



1st. It forms a weak solution of alkali which keeps in 

 any climate. 



2d. Contamination with carbon dioxide is immediately 

 apparent by formation of calcium carbonate insoluble in water, 

 whereas the alkali carbonates are soluble. 



3d. It reacts exceedingly sensitively with phenolphthal- 

 ein, much more sensitive than ammonia with the same indica- 

 tor. 



In titration of milk products, it has advantages over other 

 alkalies due to the presence in milk of 'acid phosphates of cal- 

 cium and carbon dioxide 



4th, and most important, it offers an opportunity through 

 the limited solution of CaO to prepare and standardize a solu- 

 tion, without the aid of a chemical balance. If the statement 

 of Storch holds good it also reinforces itself to make up for 

 absorption of carbon dioxide from the atmosphere. 



There is a serious discrepancy in the published reports of 

 the solubility of CaO in water at different temperatures. 

 Some work has lately been done in this direction and a sum- 

 mary up to date of the solubility at O, 100c and between fif- 

 teen and thirty is as follows: 



