30 COMMERCIAL TURPENTINES. 



ing 100.82 per cent or 37.9 normal gives a residue decidedly greater 

 than one containing 100.92 per cent of sulphuric acid, when the 

 mineral oil present is 5 per cent or less. The acid is standardized as 

 follows : 



The acid is conveniently weighed in a bulb having a capillary tube 

 at the lower end and a rather large tube with a glass stopcock in the 

 upper end, fitted with a platinum wire for weighing. The pipette 

 is filled by aid of a slight vacuum, and by closing the stopcock simul- 

 taneously with the withdrawal of the capillary from the acid the 

 lower end of the capillary is emptied and may be cleaned on the 

 exterior by wiping first with a wet and then with a dry piece of cloth. 

 The pipette thus filled and dried may be left for hours without losing 

 or gaining weight. 



After weighing, dip the capillary into about 500 cc of water in a 

 large beaker, open the stopcock, and when the acid has run out, 

 wash the pipette with water run in from the top through a rubber 

 tube and funnel. Add a slight excess of sodium carbonate solution 

 of known strength by weight (0.2 gram per gram of solution is con- 

 venient); this may be run in from a suitably arranged dropping or 

 delivery flask (weighed before and after the operation) until the 

 solution is slightly alkaline to methyl orange. Boil off the carbon 

 dioxid, allow to cool, add methyl orange, and titrate back the excess 

 carbonate with half normal sulphuric acid. Determine the specific 

 gravity of the acid with a pyknometer, calculate its normality, and 

 run in from a burette, having a long capillary delivery tube, enough 

 water to dilute it to 38 normal. 



Other procedures may suggest themselves and be preferred by 

 different operators, but of the many methods of standardization 

 tried, this one was found to be by far the most accurate and as 

 expeditious as any, ordinary care holding the error below one-tenth" 

 of 1 per cent. It is needless to say that the acid must be carefully 

 guarded against absorbing moisture from the air. Several liters of 

 the acid should be prepared at a time and it should be stored in 

 quarter or half liter bottles closed with tight-fitting glass stoppers. 



Operation. Transfer 20 cc of this acid to a Babcock bottle (one 

 having a 20 cc mark is convenient), stopper, and place in ice water. 

 After cooling, add 5 cc of the turpentine, again cool, and gradually 

 mix the contents, cooling from time to time (the temperature should 

 not be allowed to rise materially), and when the mixture no longer 

 warms up after shaking, agitate thoroughly. Then place the bottle 

 in a water bath in which the water is on a level with the acid and heat 

 to from 60 to 65 C. (140 to 149 F.) in the course of about five 

 minutes, keeping the contents thoroughly mixed by vigorously 

 shaking six or seven times. Do not stopper the bottles after tur- 

 pentine has been added. 



