The Phosphates of America. ]67 



NOTES ON STANDARD ACID, ALKALINE, AND OTHER 

 SOLUTIONS, CALLED FOR IN THIS WORK. 



In the conduct of volumetric examinations, which are frequently 

 extremely useful, expeditious and exact, it is essential that all 

 " standard " solutions be prepared and employed as nearly as pos- 

 sible at a constant temperature. This temperature should be that 

 of the surrounding atmosphere, or as cool a place as may be avail- 

 able in the laboratory, say 60 to 70 F. The liquids should be 

 kept as clear as possible, and always shaken up just previous to 

 being used. 



The indicator most commonly used in alkalimetry and acidi- 

 metry is tincture of litmus, which must be kept in open vessels, to 

 avoid its being spoiled. When employing litmus, the liquid to be 

 tested must be kept boiling for some time, in order to expel all 

 CO 2 ; and normal acid must be added as long as further boiling 

 causes the color to change back from red to purple or blue. This 

 takes a long time ; sometimes half an hour or even more. This 

 time may be saved by replacing litmus by a very dilute solution of 

 methyl-orange (sulphobenzene-azodimethyl-aniline) ; but in this 

 <?ase the liquids must never be hot, but of the ordinary temperature, 

 and none but mineral acids may be employed. The cold solution 

 of sodium carbonate is colored just perceptibly yellow by adding a 

 drop or two of the solution of methyl-orange, preferably by means 

 of a pipette; if the color is too intense, it will on neutralization 

 cause the transition into red to be less sharp. Methyl-orange is 

 not acted upon in the least by CO 2 , and when all Na 2 CO 3 has been 

 decomposed, the slightest excess of HC1 causes the yellow to change 

 suddenly and sharply into pink. The rule is, therefore, to run in 

 the normal acid quickly and with constant agitation till the change 

 of color has taken place. The opposite change of color from pink 

 to faint yellow is just as sharp when titrating mineral acids with 

 sodium hydrate or carbonate. The results are identical with those 

 obtained by litmus, but, as we have said, they are obtained very 

 much more quickly, and without heating the liquids. 



Other indicators in constant use are phenolphthalein and coral- 

 line, of which it is always useful to have a small supply. 



NORMAL SODIUM CARBONATE. 



Dissolve 53 grammes of pure, dry monocarbonate, prepared by 



