1861.] 225 



preaching in size and appearance to the crispations were produced, 

 hut in no instance did the sounds occur. Solutions of iodide of 

 ammonium and iodide of potassium did not yield sounds with an 

 electric current made intermittent by means of a contact-breaker. 

 In dilute phosphoric acid the anode enlarged, i. e. fell more flat, 

 and the cathode contracted*. 



18. Numerous experiments were made to determine the most 

 suitable composition of the electrolyte, also to ascertain the effects of 

 deficiency or excess of each of the ingredients. 1st. With regard to 

 the hydrocyanic acid and hydrate of potash, the best proportions were 

 found to be their chemical equivalents (or a slight excess of acid) ; if 

 either the acid or alkali was in much excess, the latter in particular, 

 films soon formed upon the mercury anode and stopped the action ; 

 a very large excess of the acid made the solution liable to become 

 brown and lose its phonetic capacity. 2nd. With regard to the 

 cyanide of mercury, if it was omitted, or if it was present in too small 

 a quantity, the sounds did not occur immediately upon applying the 

 electric current, but only took place after the current had circulated 

 some time (being occasionally reversed in direction), and had thereby 

 caused sufficient cyanide of mercury to be formed ; and if it was in 

 excess, the sounds were irregular and feeble. And 3rd. If the solu- 

 tion was diluted with water, the loudness of the sounds diminished, 

 and by further dilution the sounds were altogether prevented ; if the 

 solution contained less than 10 or more than 50 grains of cyanide of 

 potassium per ounce, the sounds rarely occurred. An equivalent 

 quantity of strong aqueous ammonia was substituted for the hydrate 

 of potash with equal advantage, except that the solution was much 

 more liable to decompose and become brown ; and it is probable that 

 the other alkalies might also be substituted for the potash with 

 success. When a solution becomes brown, it loses its phonetic power ; 

 but this decomposition may be prevented, or at least greatly hindered, 



* In examining these liquids, I observed that if mercury was shaken strongly in 

 a slightly decomposed mixture of 2 ounces of strong hydrocyanic acid, 1 ounce of 

 water, and 30 grains of calcined magnesia, it remained in a finely-divided state 

 during several weeks, and might be washed many times with water without the 

 globules reuniting ; a similar quantity of alumina, or 10 grains of hydrate of pot- 

 ash, was substituted for the magnesia with similar but less effectual results, which, 

 with the potash liquid, were observed only after it was partly decomposed and of 

 a brown colour. 



