208 Mr. H. Medlock on the Reciprocal Action of Metals 
results; thus proving the existence both of ammonia and nitrous 
acid in the water distilled from Thames water. 
It has long been observed that certain specimens of distilled 
water act strongly upon lead, dissolving as much as five or six 
grains in a gallon; and this circumstance has given rise to the 
opinion that soft waters in general cannot safely be conveyed 
through leaden pipes, or stored for consumption in leaden cis- 
terns. According, however, to the experiments of Professors 
Hofmann, Graham and Miller, neither the soft waters of the 
Surrey Hills, nor spring-water artificially softened, have the 
slightest action upon lead; although certain specimens of soft 
water, as in the case of the water of the Dee and of the Don, 
dissolve a considerable quantity of that metal. 
Having found in water distilled from Thames water a consi- 
derable quantity of nitrous acid, free and in combimation with 
ammonia, I was induced to study more fully the action of this 
water upon lead. Into a gallon of this distilled water I placed 
a quantity of perfectly pure and bright sheet-lead, exposing a 
surface of 560 square inches. In six hours the water became 
opake, and when shaken up was perfectly milky. The lead was 
much acted upon, and in twenty-four hours the water was filtered, 
and the quantity of carbonate of lead left on the filter amounted 
to 6:4 grains per gallon, ,4,th of a grain only remaining in solu- 
tion. Six similar experiments were made with the following 
results :— 
: Lead re- 
Quantity of Carbonate of wa Tae 
Water, Lead exposed for 24 hours. |jpaq produced. maining in 
solution. 
I. 1 gallon. 560 aquare oat 64 ers. | jth gr. 
superficial. 
II. 1 gallon. F 4°7 grs. | zsth gr. 
III. 1 gallon. + 5:0 grs. | ith gr. 
IV. 1 gallon. - 5:4 grs. | ond gr. 
V. 1 gallon. 0 5:3 grs. | ~yth gr. 
VI. 1 gallon. 4 3°9 grs. | 3th gr. 
To determine whether the action of the distilled water on lead 
is due to the presence of free nitrous acid and nitrite of ammonia, 
I made the following experiments:—The 20-gallon still was 
refilled, and to the water was added a few sticks of caustic 
potash. As soon as the water became warm, there was at the 
end of the condenser a perceptible odour of ammonia, and the 
