PROFESSOR CHRISTISON ON THE ACTION OF WATER UPON LEAD. 271 



occasions at once a dense milkiness and white precipitate, shewing the presence 

 of a large quantity of muriates. Lime and magnesia being present only in the 

 most minute proportion, it is evident that the chief base in union with the muri- 

 atic acid is soda ; which farther appears from the cubical tendency of the crystals 

 obtained by evaporation. It therefore follows, that this water contains about a 

 4500th of its weight of muriate of soda, the merest traces of sulphates and muri- 

 ates of lime and magnesia, and no carbonates of any kind. Since carbonates and 

 sulphates are the most energetic of the preventive salts usually met with in ter- 

 restrial waters, and the muriates, the only salts here present in any material 

 quantity, do not act as preventives effectually unless in at least double the propor- 

 tion observed in my analysis, it is easy to understand why the lead was so readily 

 attacked in this instance. 



When the fact of the water being poisoned with lead was clearly ascertained, 

 it was at first proposed at once to substitute iron pipes for those of lead. But Mr 

 JOHNSTON suggested that a trial should be made of a weak solution of phosphate 

 of soda, as explained above, and recommended in 1836 in my " Treatise on Poisons." 

 The experiment was accordingly tried by keeping the pipes constantly full of a 

 solution containing a 27,000th of phosphate of soda. For three weeks no improve- 

 ment took place ; but it was found that owing to a leakage in the pipe, the solu- 

 tion required to be constantly renewed, and was therefore never completely at 

 rest. As it appeared essential to secure this last condition, the leak was found 

 out, though not without difficulty, and was properly stopped. Fourteen days 

 afterwards the spring water was readmitted, and a manifest improvement was 

 ascertained to have taken place, although lead was still contained in the water. 

 The solution being replaced, another trial was made in the course of six weeks 

 more ; and sulphuretted-hydrogen then barely tinted the water. A third exami- 

 nation was made fourteen days later ; and after the water had been running for 

 some time, sulphuretted-hydrogen did not in the slightest degree affect it. The 

 last report I have from Mr JOHNSTON, dated the 27th of January, states that the 

 solution had been withdrawn for a month previously, that the water had been 

 kept running constantly for several days before it was subjected to examination, 

 and that no trace of lead could be detected in it by careful analysis. 



From the facts now detailed, together with the results of my former inquiries, 

 the following conclusions may be drawn as to the employment of lead-pipes for 

 conducting water. 



1. Lead-pipes ought not to be used for the purpose, at least where the dis- 

 tance is considerable, without a careful chemical examination of the water to be 

 transmitted. 



2. The risk of a dangerous impregnation with lead is greatest in the instance 

 of the purest waters. 



