40 TESTING MISCELLANEOUS SUPPLIES. 



before treating with benzol and ether. Some paints are very difficult to settle 

 when treated with a single solvent, and mixtures of solvents must then be tried. 

 Ma in ilia nil (Select Methods of Paint Analysis) recommends 60 volumes of 

 benzol and 40 volumes of 95 per cent wood alcohol. No system of extraction 

 will remove absolutely all the vehicle, the insoluble portion being probably 

 metallic soaps or linoxyn. 



After removing all of the soluble vehicle, dry the pigment, first at a low 

 temperature in a gentle current of air, and then at 105 C. ; weigh, and from 

 the loss in weight calculate the percentage of vehicle and pigment; then from 

 the total weight of mixed paint and the weight of clear vehicle drawn off 

 calculate the percentage of vehicle and pigment in the original paint. 



2. Analysis of Pigment. 



Follow the methods for dry colors. In general determine the amount in- 

 soluble in hydrochloric acid and the nature of the insoluble, and make an analy- 

 sis of the soluble portion. In the absence of carbon and hydrated silicates 

 (clay, etc.), a fairly close determination of unextracted vehicle may be made by 

 drying the insoluble at 105 C., weighing, and then igniting and weighing. This 

 loss is called combined water and carbonaceous matter, and in many cases may 

 be safely considered as unextracted vehicle. 



3. Analysis of Vehicle. 



Weigh 100 grams of the vehicle into a 500 cc flask, connect with a spray 

 trap and a vertical condenser, and pass through it a current of steam, first 

 heating the flask in an oil bath at 100 C. ; with the steam still passing through, 

 raise the temperature of the bath to 130. Catch the distillate in a small 

 weighed separatory funnel ; continue distillation until the funnel contains 

 300 cc of water. Let the distillate stand until separated into two layers, then 

 draw off the water and weigh the light oils. Examine as under turpentine, 

 page 13. A slight error is caused by the solubility of turpentine in water ; this 

 amounts .to about 0.3 to 0.4 cc for each 100 cc of water. 



When suflicient vehicle is available it is well to take another portion and 

 distil, without steam, placing the flask in an air bath. Note the temperature 

 of the bath at which distillation takes place, and continue the distillation at 

 a temperature of 185 C. in the air bath. This method gives somewhat lower 

 results on volatile oils than the first method, but the distillate can be tested 

 for water-soluble volatile liquids which would be lost by the steam distillation, 

 llnsaponiflable matter should be determined in this residue, or in some of the 

 original vehicle. (See examination of linseed oil, p. 13.) 



The residue Is frequently too pasty for the determination of the specific 

 gravity, which should be made on the original vehicle. Determine specific 

 gravity with a plummet or hydrometer. The small amount of suspended pig- 

 ment which frequently remains in the vehicle will introduce an error when 

 a pyknometer is used. Determine the acid number of the residue and of the 

 nal vehicle. Determine the percentage and the character of the ash 

 either from the residue or the original vehicle. The iodin number is some- 

 times a useful index ; but the constants of linseed oil which has been mixed 

 with pigments, especially lead compounds, may be so much altered that an 

 iodin number as low as 100 can not be taken as any proof of the presence of 

 other fatty oils. 



Test for ronin na described under linseed oil. Another test for rosin may 

 be nimlr l.y dissolving in carbon disulphid and adding a solution of stannic 



