XXIX] DRUGS 365 



them with more dilute solutions of standard pepsin. Thus 0.05 mg. of U. S. P. 

 pepsin can be readily detected by the nearly complete solvent action on the ricin 

 precipitate in less than 2 hours. A marked action on the ricin within the same time 

 is shown by 0.005 mg. For all practical purposes the absence of an appreciable sol- 

 vent action after 4 hours digestion indicates the absence of pepsin. Express the re- 

 sult in per cent, assuming U. S. P. pepsin to be 100% pure and calculating the 

 result according to the dilution found necessary in preparing the dilute solution 

 of the sample. 



Turpentine. 



41 color.-tentative. 



Fill a 200 cc. flat-bottomed colorimeter tube, graduated in mm., to a depth of 

 40-50 mm. with the turpentine. Place the tube in a colorimeter and place on or 

 under it a No. 2 yellow Lovibond glass. Over or under a second graduated tube 

 in the colorimeter, place a No. 1 yellow Lovibond glass and run in the same turpen- 

 tine until the color matches as nearly as possible the color in the first tube. Read 

 the difference in depth of the turpentine in the 2 tubes. If this difference is 50 mm. 

 or more, the turpentine is "standard". 



42 SPECIFIC GRAVITY.-TENTATIVE. 



20° C 

 Determine the specific gravity at -p— ^ by means of a pycnometer. The specific 



gravity may also be determined somewhat less accurately at any convenient tem- 

 perature with a plummet, correcting the result by using the factor 0.00082 for each 

 degree that the temperature of the determination differs from the standard tem- 

 perature. 



43 REFRACTIVE INDEX.-TENTATIVE. 



Determine the refractive index at any convenient temperature with an accurate 

 instrument and calculate the result to 20°C., using the correction factor 0.00045 

 for each degree that the temperature of the determination differs from 20°C. 



44 DISTILLATION.-TENTATIVE. 



Use an ordinary Engler flask (the internal diameter of the side tube must be 6-7 

 mm.) and condenser'* and heat the flask in a glycerin or oil bath'^. Fit the flask 

 with a thermometer reading 145°-200°C. Place 100 cc. of the turpentine in the 

 flask, connect with the condenser and distil. Conduct the distillation so that the 

 distillate passes over at the rate of 2 drops per second. Note the initial distilling 

 temperature and the percentage distilling below 170°C. 



POLYMERIZATION. -TENTATF/E. 



45 REAGENT. 



S8N sulphuric acid. — Mix 140 grams of concentrated sulphuric acid with suflBcient 

 liquid, fuming sulphuric acid (about 10 grams) to obtain an acid slightly stronger 

 than 38N. Determine the exact strength'* of this mixture and also of the concen- 

 trated acid as follows: Weigh out 6-8 grams in a bulb, having a capillary tube in the 

 lower end and a tube with a stop-cock in the upper end, fitted with a platinimi 

 wire for suspending on a balance. (The bulb is filled by the aid of a slight vacuum, 

 and the lower end of the capillary is emptied by closing the stop-cock simultaneously 

 with the withdrawal of the capillary from the acid; after which it is wiped off first 

 with a wet and then with a dry piece of cloth.) Run the acid into cold water, make 

 up to volume and titrate an aliquot of the solution against standard alkali or add an 



