22 TESTING MISCELLANEOUS SUPPLIES. 



is passed into the flask until it becomes about half full of condensed water, when 

 the steam is shut off and the original flask heated directly and distilled down 

 to the same small bulk this operation being conducted twice. The distillate is 

 then transferred to a special flask and 1 cc of syrup phosphoric acid added to 

 ensure a slightly acid condition. The flask is then heated and distilled down 

 to a small bulk say, 20 cc. Steam is then passed through the flask until it 

 contains about 200 cc of condensed water, when the steam is shut off and the 

 flask heated directly. These operations of direct distillation and steam distil- 

 lation are conducted until 10 cc of the distillate require but a drop of tenth- 

 normal alkali to produce a change in the presence of phenolphthalein. Then 

 the bulk of the distillate is titrated with tenth-normal sodium hydroxid, and 

 the acetic acid calculated. It will be found very convenient in this titration, 

 which amounts in some cases to 600-700 cc, to titrate the distillate when it 

 reaches 200 cc, and so continue titrating every 200 cc as it distils over. 



If the white lead contains appreciable amounts of chlorin it is well to add 

 some silver phosphate to the second distillation flask and not carry the distil- 

 lation from this flask too far at any time. 



The method used by the chemists of the Navy Department is as follows: 

 Weigh 25 grams of white lead in an Erlenmeyer flask, add 75 cc of 25 per cent 

 phosphoric acid, distil with steam to a 500 cc distillate, add to the distillate 

 some milk of barium carbonate, bring to a boil, filter, keeping the solution at 

 the boiling point (it is not necessary to wash), add an excess of sulphuric acid 

 to the filtrate and determine the barium sulphate in the usual manner ; subtract 

 53 milligrams from the weight of the barium sulphate and calculate the re- 

 mainder as acetic acid (BaSO4X0.515=CH 3 COOH). The object of this rather 

 indirect method is to avoid any error that might arise from fatty acids being 

 carried over by the steam distillation. For white lead that has not been 

 ground in oil, Thompson's method is to be preferred. 



2. Lead Zinc Whites. 



French zinc is practically pure zinc oxid, being made from metallic zinc. 

 American zinc is made by roasting zinc ores, and almost always contains some 

 lead. Sublimed lead is made by volatilizing galena, and as sphalerite is usually 

 associated with the galena, it nearly always contains zinc oxid in addition to the 

 basic sulphate of lead. Zinc lead is essentially lead sulphate and zinc oxid. 



(a) MOISTURE. 



Dry 2 grams for 2 hours at a temperature of 105 C. 

 (b) SOLUBLE SULPHATE. 



Boil 1 gram of the sample with 75 cc of water and 25 cc of alcohol, filter, 

 wash with a mixture of alcohol and water (1:3), and determine sulphuric 

 acid In the filtrate by the usual method of precipitation with barium chlorid. 

 The soluble sulphate may be calculated to zinc sulphate. 



(c) INSOLUBLE AND TOTAL SULPHATE. 



Treat 1 gram in a GOO cc beaker with 10 cc of water, 10 cc of strong hydro- 

 chloric acid, and 5 grams of ammonium chlorid, heat on a steam bath in a cov- 

 ered beaker for five minutes, add hot water to make about 400 cc, boil for five 

 minutes, and filter to separate any insoluble material. (A pure color should be 

 completely dissolved.) Wash with hot water, ignite, and weigh the insoluble. 



