10 PUBLIC HEALTH CHEMISTRY 



grammes of the salt are equivalent to I gramme of 

 hydrogen. Hence 



Non- Standardized Solutions : 



Ammonia free water. 



Organically pure ammonia free water. 



Nessler's solution. 



Methyl-orange solution (1 grm. per litre of water). 



Phenolphthalein solution (1 % in 50 % alcohol). 



Starch solution (5 grm. per litre of boiling water). 



Baryta water (5 grm. of crystallized barium hydrate in 

 1 litre of freshly boiled distilled water. Stopper and set 

 aside for three days, and decant off clear liquid. About 



Metaphenylene - diamine (5 grm. per litre aq. dest. 

 slightly acidulated with a few drops of sulphuric acid). 



Naphthylamine acetate in sulphanilic acetate : 



a. 3 to 4 grm. of sulphanilic acid dissolved in 1 litre 



of dilute acetic acid. 



b. frds grm. of naphthylamine are boiled with 150 



c.c. of aq. dest., the colourless liquid poured off 

 and diluted to 1 litre with dilute acetic acid. 



c. Mix equal bulks as required for testing. 



Phenol-sulphonic acid (32 c.c. of pure concentrated 

 sulphuric acid are added to 4 c.c. of pure phenol. Heat 

 to ioo C. for 2 to 3 hours. Cool, and add no c.c. of 

 distilled water). 



INDICATORS. 



These may be classified under two heads : 



(1) Neutrality indicators, which give a special reaction 



with acid or alkaline liquids, or with both ; (2) All others, 



such as starch, iodine, chromate of potash, permanganate 



of potash, and soap lather. 



Neutrality indicators are divided thus by R. T. 



Thompson : 



