20 Decay oj Gaspipes in certain Soils. 



self with mentioning that, apart from the influence of voltaic 

 decomposition, in which the graphite, iron and brine form the 

 circle, there are conditions which are admittedly sufiicient for 

 bringing about the change, by enlisting only the simplest 

 chemical means. Solutions of bi-carbonate of ammonium 

 and chloride of sodium produce by interchange bi-carbonate 

 of sodium and chloride of ammonium. This decomposition 

 formed the subject of a remarkable invention patented about 

 30 years since by Hemming and Dyer. On it was based the 

 process of the British Alkali Company ; and although it did 

 not succeed in an economic direction, the chemical change 

 itself can be easily demonstrated by experiment, on the small 

 or large scale, as an indisputable chemical fact. In the soil 

 and porous clays we have a supply of both ammonia and car- 

 bonic acid, so that there is nothing wanting for bringing 

 about a change of the kind considered. Moreover, the cast 

 iron is permeable to gases, and tlie contained coal gas, 

 although holding but little carbonic acid gas, is at all times 

 a source of ammonia available for the chemical decomposition 

 in point. The French chemists, investigating on behalf of 

 agriculture, have also shown how, by means quite distinct 

 from those just mentioned, common salt in a soil may be 

 dissociated so as to yield sodium salts of an organic acid. In 

 advancing these statements it is desired that the object be 

 understood as that of showing that the conditions for possible 

 chemical changes of the requisite kind do exist, and it is 

 also wished that it should be understood that no assertion 

 is advanced favouring any particular course of chemical 

 exchange as that which actually takes i^lace, of patting 

 forward any agencies as those certainly concerned in such 

 changes. 



We know quite well that a conversion of cast iron, very 

 similar to the one under notice, takes place in the sea, and 

 iron pipes or pumps drawing salt water from mines have 

 oeen found to decay from a similar cause. There is the case 

 of a pipe in a coal mine, quoted by Dr. Henry. The specific 

 gravity of the decayed pipe was 2-08 to 2 "15 5, and the water 

 of the mine contained of saline matter, chloride of sodium, 

 chloride of magnesium, chloride of calcium, sulphate of lime, 

 and bi-carbonate of lime, 64 grains to the wine pint. Of 

 course where chloride of magnesium is abundantly present, 

 the aspect of the chemistry of the case is modified. Berzelius, 

 in accounting for the corrosion under sea water, has not 

 included the chlorides among the agents concerned ; but to 



