578 TROPICAL HYGIENE, SANITATION, ETC. 



Add a few drops of ammonium sulphide to the remainder in the 

 casserole and a red colour will form in clouds on the surface. 



Salicylic Acid. 



Prepare a solution as for benzoic acid test, but 50 grm. only. 



Divide solution into two portions as benzoic acid and salicylic acid 

 are often present together in the same supply. 



Wash twice with one-tenth of its volume of water when one has 

 prepared the other extract as for benzoic test. 



The washing is to get rid of the mineral acid as the test is much 

 more delicate in its absence. 



Evaporate ether in porcelain dish. 



To residue add two drops of dilute (i per cent.) ferric chloride 

 solution. 



Or better, three to four drops of ferric alum solution. 



Rub it around with a glass rod. 



A violet colour is positive for salicylic acid. 



If positive confirm by another test as several other organic sub- 

 stances give the coloration. 



To the solution to be tested add four to five drops of a 10 per cent, 

 solution of potassium or sodium nitrite. 



Add four to live drops of acetic acid. 



Add one drop of ro per cent, solution of copper sulphate. 



Heat to boiling. 



A reddish tinge is positive for salicylic acid. 



There may be sufficient to give a blood red. 



Phenol gives the same reaction but benzoic acid does not. 



As salicylic acid occurs naturally in some fruits not more than 

 50 grm. of the substance to be examined should be taken. 



This is known as the Jorissen test. 



Boric Acid and Borax. 



The turmeric paper test is useful. 



Take 25 grm. of the sample. 



Make distinctly alkaline with sodium hydroxide. 



Evaporate to dryness in a porcelain dish. 



Boil Avith 15 c.c. of water. 



Add hydrochloric acid until acid to litmus paper, then add ten drops 

 more acid. 



Filter and evaporate to dryness on the water bath with a piece of 

 turmeric paper partly immersed in the fluid. 



Cherry red colour of the paper is positive for boric acid and borax. 



The colour changes to a bluish green by a drop of ammonia. 



A quantitative test should be carried out because boric acid occurs 

 in apples and other fruits and vegetables in nature in minute quantities. 

 It occurs in greater quantities in common salt. 



