1904] of Acids and Bases in respect of Paramcecium aurelia. 101 



difference was established between platinised electrodes immersed in 

 the acid and alkaline solutions employed. 



The action of acids and bases upon Paramcecia is shown in Tables I 

 and II. The acids employed are divided into three groups, according 

 to the degree to which they are dissociated; the first consisting of the 

 strong mineral acids, hydrochloric, nitric and sulphuric;, the second 

 including the organic acids, formic, lactic, oxalic, tartarie, citric and 

 acetic, together with phosphoric acid ; while the third group is made 

 up of extremely weak electrolytes, namely, carbonic, carbolic, hydro- 

 cyanic and boric acids. Similarly the bases employed may be arranged 

 in three groups : the first consisting of the strongly dissociated metallic 

 alkalies; the second being represented by the feebly dissociated 

 ammonium hydrate ; and the third consisting of the extremely weak 

 electrolyte anilin. In the second column of the tables, the figures in 

 brackets represent the time, in minutes, which elapsed before all the 

 Paramcecia employed were killed. The latter were added in the 

 proportion of about thirty to every. 10 c.c. of liquid, and did not 

 appreciably affect the concentration. The temperature of experiment 

 was 16 C. to 18 C. 



In 0*0001 N concentration* the strong mineral acids are nearly 

 equally lethal. Some of the weak acids of the second group, in the 

 same concentration, are more lethal than the mineral acids, namely, 

 acetic, lactic and oxalic acids ; while others of the same group are less 

 so, namely, phosphoric, citric and acetic. On the other hand the weak 

 electrolytes are lethal in a considerably higher molecular concentration, 

 reaching in the case of hydrocyanic acid 0'3 N. 



Since the rate at which chemical change takes place is dependent 

 upon ionic concentration, the dissociation co-efficient calculated from 

 the conductivity (18 C.) or the dissociation constant (25 C.) is given, 

 so far as the available data permit, in the third column of the tables, 

 and the corresponding ionic concentration in the fourth column, the 

 latter being the product of the concentration and dissociation 

 coefficient. 



The weak acids are more lethal in less ionic concentration than the 

 strong acids, and the extremely weak electrolytes exhibit the smallest 

 ionic concentration, that of phenol forming the limit of the series. 

 Excluding phenol, however, it is seen that when the acids employed 

 are arranged in the order of their dissociation (Table I), the diminution 

 in ionic concentration proceeds at a much slower rate than the increase, 

 of molecular concentration. 



The strong alkalies are similarly less toxic than the weak alkali, 

 ammonium hydrate, and the latter again is considerably less so than 



* The concentration given in the tables is equivalent, except for carbonic and 

 boric acids, which are regarded as binary compounds, and whose concentration 

 represents gramme-molecules per litre. 



