308 



the latter and more frequent case it may be oxalate of lead, a 

 supposition which will be confirmed by incineration (page 298), 

 when malate of lead will leave 56"91°/o oxyd of lead. Should 

 the result be at variance with this supposition, and even be 

 confirmed by a second incinei'ation, the elementary analysis is 

 resorted to and the propei'ties of the acid must be investigated. 

 To perform this, triturate a portion of the lead-compound with 

 water to an impalpable pulp, wash it into a glass-jar, impregnate 

 the milky liquid under continual stirring with well-washed 

 sulphuret of hydrogen, allow the excess of the latter to evaporate 

 at the air, filter oflT the sulphide of lead, after it has completely 

 subsided (which takes sometimes a very long time, and may be 

 accelerated by gently heating), evaporate a part of the filtrate at 

 a very gentle heat (to prevent ethei'ification of the alcohol) and 

 at last under the receiver of the air-pump, and employ the other 

 ])art of the filtrate for testing with solution of baryta, lime-water, 

 (fee, and for the preparation of some other salts, while the dry 

 acid is tried on its behaviour in the heat, &c. 



If there is reason to suppose that the water has withdrawn 

 more than one compound from the lead precipitate, these com- 

 pounds must be separated from each other by crystallization, and 

 examined separately in the above manner. 



§• The small portion of the lead pj'ecipitate, left undissolved hy 

 hot water, is tried moist by shaking with acetic acid of about 

 20°/q. If it prove soluble and completely so when heated, the 

 further examination is confined to No. 1. If it remains turbid, 

 it must be filtered and saturated with ammonia; should it now 

 remain clear, then nothing has been dissolved by the acetic acid, 

 and it has then to be examined under No. 2. 



If, on the other hand, a turbidity has been produced by ammo- 

 nia in the acid filti-ate, the whole of the precipitate is transferred 

 from the filter into a beaker by means of a horn-knife. Then 

 mix with acetic acid to a thin pulp, cover the vessel with a 

 glass plate, agitate the contents assiduously and apply, if neces- 

 sary, a gentle heat. Filter after about an hour and wash with 

 Avater until the latter passes ofi" nearly void of acid reaction, and 

 examine separately the solution in acetic acid under 1, and the 

 undissolved remnant under 2. 



1. Add to the solution in acetic acid, carefully and under con- 

 tinual stirring, ammonia in such a quantity as to leave the acid 

 very slightly in excess (an excess of ammonia must be connected 

 eventually by a few drops of acetic acid.) This causes the part 

 iß) of the precipitate, dissolved in the acid, to separate again. 

 Let subside, collect on a filter, wash completely with water, 

 spread half of the precipitate thinly on a glass or porcelain plate, 

 dry at the air or at a very gentle heat, triturate and reserve for 

 further use. 



