ACETATES AND THEIR MANUFACTURE. 281 



tion is filtered and evaporated until a crystalline film is formed. 

 This method is, however, expensive. 



The method by double decomposition may be recommended 

 for preparing the neutral acetate on a small scale, but not for 

 manufacturing purposes. Sulphate of copper (125 parts) and 

 sodium acetate (136 parts) decompose each other, neutral cupric 

 acetate crystallizing out while sodium sulphate remains in solution. 

 The yield is, however, somewhat smaller than theoretically might 

 be expected, because the sulphate of copper is not entirely insolu- 

 ble in sodium sulphate solution. By this process the object is 

 quickly accomplished and for this reason is decidedly to be pre- 

 ferred to the following : Sulphate of copper (125 parts) and nor- 

 mal lead acetate (190 parts) decompose completely only in dilute 

 but not in concentrated solutions. Hence strong evaporation is 

 required whereby acetic acid is lost. Further, with the use of 

 lead acetate some of the newly formed lead sulphate is obtained in 

 solution ; but the lead cannot be separated with sulphuretted 

 hydrogen because the latter would decompose also the copper salt. 

 The disadvantage of substituting calcium acetate for the lead 

 acetate is that it is not crystallized and hence furnishes no ex- 

 ternal criterion of purity ; in fact it always has a slightly varying 

 composition. If a small excess of calcium salt has been used, the 

 latter, after the calcium sulphate is filtered off and the solution 

 evaporated, does not remain in the mother lye, but crystallizes 

 out as double salt (see below), together with the copper salt. 

 Since these acetates create difficulties, and as each of them must 

 first be prepared by the manufacturer by means of acetic acid, it 

 would seem more rational to directly use this acetic acid for dis- 

 solving the cupric oxide, whereby no by-products of little value, 

 such as sulphate of lead, calcium and sodium, are formed. 



The evaporation of the solution of cupric acetate obtained by 

 any of the above methods is effected in a copper boiler over an 

 open fire, or, still better, by steam. It is recommended to close 

 the boiler so that the escaping vapors of water and acetic acid 

 are condensed in a worm. Independently of the fact that by these 

 means the escaping acetic acid is regained and can be used for 

 other purposes, a great advantage is that the air of the workroom 

 is thereby not contaminated by flying particles of salt. 



