WRITING INKS. 41 



bromid or chlorid in carbon disulphid. Use a wbite porcelain dish. If no 

 water is present in either solution the presence of rosin is shown by the ap- 

 pearance of a violet color. This test is not as delicate as the Liebermann- 

 Storch test described under linseed oil. 



When much lead is present it may be lost in ashing, and for a correct de- 

 termination of metals the following method is best: Place 25 grams of the 

 vehicle in a 500 cc separatory funnel, dilute with 25 cc of a mixture of equal 

 parts of gasoline and turpentine, add 50 cc of nitric acid (1 : 1), and let stand 

 one hour, shaking every ten minutes. Then immerse the funnel in hot water, 

 loosen the stopper, and shake gently. This drives off nearly all the gasoline. 

 Remove from the hot water, let it separate, draw off the lower layer, and wash 

 the upper oily layer four or five times with warm water. Add the washings 

 to the main acid portion and determine the metals in the ordinary manner. 

 If the paint is enamel paint, treat the vehicle as a varnish. (See page 18.) 



INKS. 

 WRITING INKS. 



Almost without exception all black inks suitable for record purposes are 

 iron-tannin inks. The determinations of an analytical character which are of 

 value are as follows: 



1. Specific Gravity. 



Determine with a pyknometer at 15.5 C. 



2. Total Solids. 



Weigh 10 grams of ink in a flat-bottomed platinum or porcelain dish, evapor- 

 ate to dryness on the water bath, and then heat in an oven at the temperature 

 of boiling water for two hours ; cool in a desiccator and weigh. 



3. Ash. 



Burn the residue from the determination of total solids at a low temperature, 

 preferably in a muffle. In order to avoid loss by foaming the dish used should 

 not be too small, not less than 50 cc capacity. 



4. Iron. 



Transfer the ash to a small beaker and dissolve in 15 cc of hydrochloric acid 

 with the addition of staunous chlorid at the temperature of the steam bath ; 

 reduce by adding stannous chlorid, drop by drop, to the hot solution until the 

 color is destroyed, and then add one or two drops in excess. Wash the reduced 

 iron solution from the small beaker into a 600 cc beaker and dilute to about 

 250 cc with cold water, add all at once an excess of mercuric chlorid, stir, allow 

 to stand a minute, and titrate with standard potassium dichromate solution. 



5. Sulphuric Anhydrid (SO 8 .) 



Determine both iron and sulphuric anhydrid in the same sample. Place 

 from 10 to 15 grams of ink in a platinum dish, add 1 to 1.5 grams of sodiuin 

 carbonate previously dissolved in water, evaporate to dryuess, ash, extract 

 with water, add bromin water to the extract, boil, render acid with hydro- 

 chloric acid, boil off the bromin, and determine the sulphuric anhydrid (SO) 



