317 



The remaining liquid, mixed with the water that has been used 

 for washing and evaporated again to the original weight of 100 

 grams, or the original aqueous solution reduced to the same 

 weight — after no crystals have been obtained from it — is 

 examined in small quantities with the reagents indicated under 

 II., B,d. 



After these experiments have been made, precipitate and treat 

 the remaining liquid as under II., B, e, f, g, successively with 

 acetate of lead, ammonia and subacetate of lead, and examine 

 the precipitates as indicated there. 



The precipitate (e), obtained by acetate of lead, may in this 

 case contain, besides the substances indicated there, gum and 

 a protein-substance not identical with albumin. These substances 

 will remain with the sulphide of lead as insoluble in alcohol. To 

 ascertain their presence, wash the sulphide of lead well with 

 alcohol, dry at 100°, triturate and shake with cold water. This 

 dissolves the gum readily, and leaves behind the protein-substance 

 rendered insoluble in water by drying and heating. The pi-esence 

 of gum in the cold water will be recognised by its forming 

 on evaporation an amorphous tasteless varnish. 



After this, digest the sulphide of lead with phosphoric acid of 

 1"04, warm, filter, edulcorate the remaining sulphide of lead with 

 water, and neutralise the whole filtrate carefully by means of an 

 alkali. The protein-substance is thrown down; collect it on 

 a filter, wash, dry at 110°, and determine its weight. The 

 quantity of the substance obtained hereby is insufiicient for 

 a closer investigation. 



If no gum or protein-su^bstance has been found in the lead- 

 precipitate e, the lead-precipitates / and g have to be tried for 

 it, and this is done with the precipitate /in the same manner as 

 with precipitate e, whereas the precipitate g, its decomposition 

 not being efiected under alcohol but under water, is treated in the 

 following way: — Boil the liquid, filtered ofi" from the sulphide of 

 lead and containing the gum, and probably the protein-substance, 

 for a few minutes, when the protein-substance, if present, will 

 separate; filter, evaporate to a small bulk, and shake a sample of 

 the liquid with alcohol of 90%. If the mixture remains clear, 

 no gum or protein-substance is present; if it becomes turbid, 

 pi'ecipitate the whole liquid with alcohol, wash the sediment with 

 alcohol, dry at 100°, and treat with cold water. A clear solution 

 contains only gum; any insoluble portion is protein-substance. 

 As the sulphide of lead might in this case as well contain 

 protein-substance, it must be treated as above, with phosphoric 

 acid, &c. 



The liquid, after separating from the precipitate, produced 

 by lead- vinegar, is treated according to II., B, h. 



