METHODS OF ANALYSIS, 17 



Bunsen flame, or better, in a muffle at a very low heat. When all carbon has disap- 

 peared, cool the dish in a desiccator and weigh quickly. Find the per cent of total ash 

 i by dividing the weight by 5 and multiplying by 100. In case the last traces of carbon 

 I are hard to burn, add a little water, evaporate, and then reheat or burn . Note the color 

 of the ash. 



Soluble and insoluble ash. To the platinum dish containing the total ash add 40 cc 

 of hot water and boil gently for two minutes, using care to avoid spattering. Filter 

 through a small ashless filter and wash with hot water until the filtrate amounts to about 

 100 cc . Retain the filtrate for determining the alkalinity of the soluble ash . Transfer 

 the filter paper containing the insoluble ash to the same platinum dish and carefully 

 ash at a low red heat, as before. Cool and weigh. The increase in weight over the 

 platinum dish is due to the insoluble ash. Divide this quantity by 5 and multiply by 

 100 and the percentage obtained is the insoluble ash. Subtract this per cent of insolu- 

 ble ash from the per cent of total ash and the result is the per cent of soluble ash. Save 

 the platinum dish with the insoluble ash for the determination of the alkalinity of 

 insoluble ash. 



Alkalinity of soluble ash. Transfer the 100 cc of water solution from the preceding 

 determination to a beaker or porcelain evaporating dish and determine the alkalinity 

 by titrating with tenth-normal hydrochloric acid, using methyl orange as an indicator. 

 The number of cubic centimeters of acid used divided by 5 gives the number of cubic 

 centimeters of tenth-normal acid necessary to neutralize the ash of 1 gram of sample, 

 which figure multiplied by 100 is used to express the alkalinity of the soluble ash. 



Alkalinity of insoluble ash. To the platinum dish containing the insoluble ash add 

 an excess of tenth-normal acid (usually 5 cc) and about 30 cc of water. Heat gently 

 until solution is complete. Cool and titrate with tenth-normal sodium hydroxid, 

 using methyl orange as an indicator. Subtract the number of cubic centimeters of 

 tenth-normal alkali used from the number of cubic centimeters of acid and the 

 remainder will be the number of cubic centimeters of acid used to neutralize the 

 insoluble ash. This number divided by 5 and multiplied by 100 gives the alkalinity 

 of the insoluble ash. 



LEAD NUMBER. 



Two determinations of the lead number were made, one using the ordinary basic 

 lead acetate solution and the other using normal or neutral lead acetate solution for 

 the precipitation. The procedure was the same in each case. 



Standard lead subacetate solution. Boil 430 grams of normal acetate and 130 grams 

 of litharge, for half an hour, or boil 560 grams of Home's dry lead subacetate, with 

 1,000 cc of water; cool the mixture; allow to settle and dilute the supernatant liquid 

 to 1.25 specific gravity. To a measured amount of this solution add 4 volumes of 

 water and filter if not perfectly clear. The solution should be standardized each time 

 a set of determinations is made.& 



Standard normal lead acetate solution. Dissolve 82 grams of lead acetate in 1,000 cc 

 of water. Filter, if not clear. 



Description of method. Weigh 25 grams of the sample and transfer to a 100 cc flask 

 with water. Add 25 cc of the standard lead acetate solution (either sub or normal) 

 and shake; fill to the mark, shake, and allow to stand at least three hours before 

 filtering. From the clear filtrate, pipette off 10 cc to a 250 cc beaker, add 40 cc of 

 water and 1 cc of concentrated sulphuric acid; shake and add 100 cc of 95 per cent 

 alcohol. Let stand over night, filter on a tared Gooch crucible, wash with 95 per 



a Unless the directions for preparing the basic lead acetate are carried out with 

 great care and exactness it is better to use the Home's dry lead subacetate. 

 & J. Amer. Chem. Soc., 1906, 28 : 1204. 

 48874 Bull. 13410 2 



