DETECTION OF PRESERVATIVES. 63 



case. The analyst should then select the tint which to his eye seems 

 to be most characteristic. 



In this laboratory the lightest shade of pink, spreading over the 

 entire surface of the turmeric paper, has been chosen as the standard, 

 and is used for comparison. For the determination, 50. cc of the 

 sample under examination are made slightly alkaline with limewater, 

 evaporated to dryness, and ignited. Three cc of water are then added 

 to the ash and half -strength hydrochloric acid, drop by drop, until an 

 acid reaction is obtained. The volume of acid so added is noted and 

 enough dilute hydrochloric acid (1 part of the concentrated acid to 5 

 parts of water) is then added to make the total volume of the liquid 5 

 cc, the whole thoroughly mixed, and a drop tested with turmeric 

 paper. . If the boric-acid reaction is heavier than that adopted as the 

 standard, the solution should be diluted with dilute hydrochloric acid 

 (1-15) until the reaction approximates the shade of the standard. 

 From the dilution the approximate percentage of boric acid in the 

 original sample may be calculated. 



DETECTION OF FLUORID. 



First method. About 100 grams of the sample, made slightly alka- 

 line with ammonium carbonate, are heated to boiling and the fluorin 

 precipitated with a few cubic centimeters of calcium chlorid solution. 

 The boiling is continued for five minutes after the precipitation, the 

 precipitate removed by filtration, washed with a little water, dried, 

 and ignited in a small platinum crucible. One cc of strong sulphuric 

 acid is added, the crucible is covered with a watch glass coated with 

 paraifin or wax, with a character marked through the wax so as to per- 

 mit the watch glass to be etched at some point, and heated on a water 

 bath for an hour at a temperature of from 75 to 80. One mg. can 

 be readily detected by this method. 



Second method. If it is desired, the preceding method may be varied 

 by mixing a small amount of precipitated silica with the precipitated 

 calcium fluorid and placing it in a crucible covered by a watch glass 

 which is not coated with paraffin, and. to which a drop of water is sus- 

 pended on the underside. One cc of concentrated sulphuric acid is 

 added to the crucible, which is then heated for an hour at the tem- 

 perature of 70 or 80. The silicon fluorid which is formed is decom- 

 posed by the water, leaving a gelatinous deposit of silica, while a ring 

 is frequently etched at the circumference of the drop of water. 



DETECTION OF BOROFLUORIDS AND SILICOFLUORIDS. 



About 200 cc of wine are made alkaline with limewater, evaporated 

 to dryness, and incinerated. The crude ash first obtained is extracted 

 with water, to which sufficient acetic acid has been added to decom- 



