HOME-MADE LEAD ARSENATE. 13 



exist, as there are at the present time twenty or more firms in different 

 parts of the United States which manufacture it, and it is possible 

 to procure it in almost any section of the country. Only those 

 brands should be accepted, however, which bear the guaranty of a 

 reliable manufacturer on the package. When such can not be 

 obtained at a reasonable price, or if only a small amount is needed, 

 it may be advantageously made at home by following the directions 

 which are given herein. Again, in some cases where a large quantity 

 is to be used and the proper chemicals can be purchased at a reason- 

 able price, a considerable saving might result by making it at home, 

 but this would probably not be advisable as a general rule. In the 

 making of such a product there is always some risk due to poor chem- 

 icals, an incorrect formula, or carelessness in making. The chemicals 

 used in its preparation are sodium arsenate and either lead acetate 

 or lead nitrate. All of .these can be easily obtained from druggists 

 and are the cheapest compounds containing the necessary elements 

 in a suitable form. The wholesale prices of the technical grades of 

 these chemicals at the present time are: Lead acetate, 7J to 8 cents 

 per pound; lead nitrate, 7f to 8| cents per pound; sodium arsenate, 

 5? to 6 cents per pound. These salts all show some variation in their 

 composition and at times this may be very great, particularly in the 

 case of sodium arsenate, which is the salt used to supply the arsenic. 

 Samples of these chemicals have been obtained in various parts of the 

 country from druggists and other sources and subjected to analysis. 

 In the lead salts the total amount of lead oxid has been determined 

 and in the sodium arsenate total arsenic oxid and chlorin. These are 

 the only substances which it is necessary to consider, as they are the 

 ones that enter into the reaction. 



METHODS OF ANALYSIS. 

 LEAD SALTS. 



Total lead oxid. This may be determined as sulphate by precipi- 

 tating with sulphuric acid, or as oxid by precipitating with ammonia 

 and ammonium carbonate and converting into the oxid by ignition. 

 The details of these methods are given in works on quantitative anal- 

 ysis and both give satisfactory results. 



SODIUM ARSENATE. 



Total arsenic oxid. Dissolve 2 grams of the sample in water and 

 make volume up to 250 cc. Heat 50 cc of this solution to about 

 80 C., add 3 grams of potassium iodid and 50 cc of concentrated hy- 

 drochloric acid. Let stand fifteen minutes, cool, add approximately 

 tenth-normal sodium thiosulphate solution just to disappearance of 

 color caused by free iodin. (The end point is easy to obtain without 

 the use of starch.) Add immediately sodium carbonate until most 

 of the acid is neutralized, then after all the sodium carbonate has 



