by the Immersion of unequally Heated Metals in Liquids. 17 



with the liquid pre-boiled; same result. Added 1 drachm of 

 pure sulphuric acid to this solution and retried; same result, 

 but in a very much greater degree. Same solution pre-boiled 

 gave similar results. Tried again with 4 ounces of distilled 

 water and 100 grains of the salt pre-boiled ; same result. 



79. Nitrate of Copper. — 5 ounces of spring water and 110 

 grains of nitrate of copper ; hot metal negative. Retried with 

 the liquid pre-boiled ; same result. Acid reaction. 



80. According to these results, hot platinum is negative to 

 cold platinum in the following liquids : — moderately dilute ■= 

 aqueous solutions of boracic, phosphoric, sulphuric, hydrochloric, 

 nitric, oxalic, acetic, tartaric, and citric acids. Also in aqueous 

 solutions of the following salts : — sulphate, hydrochlorate, and 

 nitrate of-qmmonia, sulphate of soda, sulphate of alumina, sul- 

 phate of zinc, suli)hate of copper, sulphate of copper acidulated 

 with sulphuric acid, and nitrate of copper. And hot platinum 

 is positive to cold platinum in aqueous solutions of ammonia, 

 carbonate of ammonia, potash, carbonate, sulphite, sulphate, 

 chlorate, and nitrate of potash, cyanide of potassium, soda, car- 

 bonate, biborate, diphosphate, and hyposulphite of soda, chloride 

 of sodium, nitrate of soda, and microcosmic salt. 



81. In every case [provided chemical action u-as completely or 

 sufficiently excluded) where the liquid was strongly acid to test- 

 paper, h-ot platinum was decidedly negative to cold platinum ; 

 and in every case where the solution was strongly alkaline, it 

 was as decidedly positive. Also in every case where the liquid 

 was neutral, or exhibited but feeble acid or alkaline reaction with 

 test-paper, the current obtained was very feeble, and was affected 

 by very slight circumstances, so that the results in such cases 

 are necessarily less certain and less to be relied upon than in 

 the more definite ones. We may select from amongst those 

 examined the following solutions as being of the less certain cha- 

 racter : — hydrochlorate of ammonia, sulphite, sulphate, chlorate, 

 nitrate, and tartrate of potash (bitartrate of potash was also 

 feeble), diphosphate, hyposulphite, sulphate, and nitrate of soda, 

 chloride of sodium (bitartrate of soda was also feeble), and sul- 

 phate of zinc. 



8a. Thus, speaking in general terms, liable, as we have seen, 

 to some slight exceptions, we may say that hot platinum is nega- 

 tive to cold ])latinum in acid liquids, and positive to it in alkaline 

 ones ; the only exceptions to this statement amongst the instances 

 given are aqua-rcgia and dilute hydrocyanic acid, in which the 

 hot plate was positives ; sulphate of soda, which exhibited neutral 

 reaction, and yet in which the hot metal was negative, though 

 very feebly ; and bitartrate of soda, in which, although of acid 

 reaction, the hot metal was feebly positive. On account of the 



Phil. May. S. 4. Vol. 13. No. 83. Jurt. 1857. C 



