307 



sence of an alkaloid need not be doubted any longei' ; but even if 

 the result be only positive with some of them, an alkaloid might 

 be present. The behaviour to caustic alkalies has shown in some 

 degree, if it be volatile, and the closer examination is carried on 

 according to section X. As to non-volatile alkaloids, see below, 

 under h. 



(e) After having tried the tests under d, proceed to the dis- 

 covery of the 07-ganic acids contained in the liquid B. For this 

 purpose precipitate the remaining aqueous liquid (to which the 

 sample ti'eated with acetate of lead may be added) with acetate of 

 lead in excess, collect the precipitate, after it has subsided, on a 

 filter, and edulcoi'ate with water, as long as it assumes an acid 

 reaction towards litmus-paper. (Testing with sulphuretted hydro- 

 gen in order to find out when washing is finished, is inadmissible, 

 because most of these lead-precipitates are not quite insoluble in 

 water). Should the precipitate begin to decompose during washing, 

 (if the water running off becomes suddenly milky), the washing 

 must be finished, even if the acid reaction has not yet disapjjeared. 

 The filtrate and the water used for washing are reserved fory! 



From the washed precipitate take with a glass-rod a sample of 

 about the size of two peas, put the rod into a test-tube, add 4 to 

 5 grams water, and heat to the boiling-point. A clear solution 

 obtained hereby shows that only acids are present, the lead-com- 

 pounds of which are soluble in hot water*, as, for instance, nudic 

 acid, and the precipitate has then only to be examined under a. 

 (If a complete solution can be expected, has already been ascer- 

 tained by the preliminary reactions under d, for a complete 

 solution could not have been effected in the presence of sulphuric, 

 phosphoric, oxalic, tannic, citric, and of many other acids.) If, on 

 the contrary, the liquid remains turbid, it is filtered boiling hot, 

 without washing, and the filtrate is left to cool. If no sediment 

 (crystalline or pulverulent) is obtained, the liquid is concentrated 

 and again left to stand cold. If no sediment has formed now, 

 proceed to B, since the precipitate does not contain any organic 

 acids such as yield lead-compounds soluble in hot water. 



On the other hand, if a sediment has been obtained in the above 

 way, the whole precipitate is washed off the filter into a spacious 

 porcelain-dish under addition of water ten times the volume of 

 the moist precipitate. Heat under continual stii-ring with a glass- 

 rod, or with a porcelain-spatula, for a quarter of an hour; filter hot 

 and wash with hot water. The filtrate is now examined under a, 

 and the insoluble remnant under ß. 



a. Free the aqueous solution from the sediment produced in the 

 cold, evaporate to a small bulk, collect the solids which may have 

 separated on a filter, wash with a little cold water and dry. The 

 mere external appearance of the substance will teach already to 

 some extent, whether it is of a complex constitution or not. In 



X 2 



