452 REPORTS ON THE STATE OF SCIENCE. 



form homogeneous combinations, but rather by a mechanical interposi- 

 tion of the molecules of the two salts with those of the water. 

 -.opt- Riidorff" 7 published further results of work on the lines of 



that previously recorded (1873), and concluded that those salts 

 which are isomorphous or which form together double salts, displace one 

 another from their solutions, while those salts which do not crystallise 

 together do not displace each other from solution. In the following year 

 -.sop there appeared the first of a series of publications by Engel, 121 



dealing with the somewhat complex case of the solubility of 

 cupric sulphate in presence of ammonium sulphate. This was soon 

 followed by an account 121 of experiments on the precipitation of 

 barium, sodium, ammonium, and strontium chlorides by hydrogen 

 chloride. The conclusion drawn being that the solubility of chlorides 

 which are precipitated from their aqueous solutions by hydrogen 

 chloride became diminished in presence of the acid by the amount 

 which corresponds to one equivalent of chlorine for each equivalent 

 of hydrogen chloride; thus the number of equivalents remaining in 

 solution keeps practically constant. In all cases, except with 

 ammonium chloride where the sum of the equivalents' slightly but 

 continuously increases, the sum of the equivalents was found to be 

 diminished somewhat at first and then incr-eased. This law of 

 equivalent precipitation was only found to hold good up to the point 

 where the solubility of the chloride had become reduced to about £ of 

 its solubility in water. These conclusions of Engel were adversely 

 criticised by Jeannel 122 who enunciated the law that the solubility of 

 chlorides in water in the presence of hydrogen chloride varies in such 

 a manner that the sum of the equivalents of salt, acid, and water in 

 the solution remains practically constant at the same temperature, 

 irrespective of the nature of the chlorides. 

 1W To this Engel 126 replied by publishing results of precipitating 



magnesium chloride by hydrogen chloride which supported his 

 previous conclusions, although he found some deviation from his equi- 

 valent precipitation law with higher concentration of HC1, and also 

 when barium chloride or strontium chloride were the salts employed. 

 This third paper on the effect of hydrogen chloride on the solubility 

 of chlorides dealt with cases of various anhydrous and hydrated 

 salts, and contained results quite in harmony with his law of equivalent 

 precipitation. Similar results were obtained with nitric acid and 

 nitrates. A further publication 126 recorded the behaviour of sulphuric 

 acid as a precipitant for sulphates. In this case, however, the acid be- 

 haved as though one equivalent withdrew, or prevented twelve equiva~ 

 lents of water from exerting any solvent action, and the corresponding 

 quantity of salt was precipitated. As with hydrogen chloride this did 

 not hold with strong acid solutions. 



In the next year Engel 139 published a series of three 



memoirs treating of the solubility of salts in presence of acids, 

 bases, and salts. The first 139 being a general review of the subject ; the 

 second 139 relating to the solubility of carbonates as influenced by 

 carbonic acid, and also that of oxalates influenced by oxalic acid ; the 

 conclusion arrived at being that the law of Schloesing 51 (Section V, 



