266 PROFESSOR CHRISTISON ON THE ACTION OF WATER UPON LEAD. 



since I first wrote on this subject, as to the exact nature of the substance formed 

 by the action of water upon lead. 



The first fact to be mentioned has been already briefly alluded to by me in a 

 former publication in 1836.* But its circumstances appear to merit a more de- 

 tailed statement. 



A few years ago, the water of a spring was introduced into the mansion of 

 Dalswinton in Dumfriesshire, by a lead-pipe, from a distance of three-quarters 

 of a mile. While on a visit there in the autumn of 1834, only a few days after 

 operations were finished, and the water was flowing into the great cistern for sup- 

 plying the house, my attention was called one morning by one of the guests to 

 the water-bottle on his dressing-table, and a tumbler of water which had been 

 poured from it. The bottle was lined with a thin white incrustation of a pearly 

 lustre ; and the water, which had stood some time exposed to the air, presented 

 a thin film of the same appearance over its whole surface. The cause being at 

 once suspected, we proceeded with our host, Mr LENY, to examine the great cis- 

 tern into which the water was discharged directly from the pipe. Here we found 

 the water entirely covered with a similar film, and the bottom and sides of the cis- 

 tern lined with a loose pearly Avhite incrustation, in such quantity as to appear as 

 if painted with white paint. It was also remarked, that water fresh drawn from 

 the pipe was perfectly transparent at first, but, on exposure to the air, quickly 

 presented the white film seen in the tumbler. It needs scarcely be stated, that 

 the appearances now mentioned were recognised as the result of the action of the 

 water on the lead of the pipe. And it may be added, that the white substance 

 was afterwards ascertained to be a carbonate of lead. 



I confess that the observations thus made surprised me not a little. For 

 being told, the previous autumn, that it was proposed to bring into the house in 

 lead-pipes the water of this spring, which had long enjoyed a high character in 

 the neighbourhood for purity, I made an experiment for the purpose of discover- 

 ing whether it could be safely conveyed in lead ; and finding that several pieces of 

 fresh-cut lead retained their lustre almost untarnished when immersed for four- 

 teen days in a tumbler of the water, I concluded that it contained salts enough to 

 prevent corrosion of the lead. I did not at the time advert to the difference be- 

 tween an experiment in which some ounces of water were left at rest on a few 

 square inches of lead, and one in which a column of water only three-quarters of 

 an inch in diameter flowed constantly over a surface of nearly 800 square feet. 



The means of clearing up the cause of the action, by analyzing the water, 

 were not within my reach. It was presumed, however, from the general princi- 

 ples established by previous inquiries, that the reputation of the spring for extra- 



* Treatise on Poisons, third edition, p. 489. 



