1814.] On Rain IVater. 141 



On my mentioning the circumstance of the lilac infusion to my 

 ingenious friend Mr. Robert Higgin, he suggested the probability 

 of its being caused by the presence of ammonia, which he sup- 

 posed was formed by the combination of nitrogen and hydrogen in 

 the atmosphere ;* this might be absorbed and brought down by 

 the rain in sufficient quantity to produce the effect. 



I was so well satisfied with Mr. Higgin's hypothesis, that it 

 was some days before I attempted to prove the cause of this extra- 

 ordinary phenomenon ; not believing that lime could ever exist in 

 the atmosphere. 



To ascertain what it really was that produced this surprising 

 effect, I made the following experiments on the water : — 



A quantity of it was heated in a retort, and a stream of muriatic 

 acid gas made to pass into a receiver, in which the beak of the re- 

 tort was placed ; but no dense clouds were produced. On exa- 

 mining tiie water which had been heated, I observed a slight pre- 

 cipitate ; and, in consequence, boiled the water till about half of it 

 Avas evaporated, and ihen found a copious precipitate. Next, a 

 quantity of water impregnated with carbonic acid was added to the 

 water that had been boiled, which soon re-dissolved the precipi- 

 tate : by expelling the carbonic acid by boiling again, it caused 

 the same precipitate as before. 



These experiments convinced me that the lilac colour which was 

 extracted from the logwood, by the rain-water that fell when there 

 had been no thunder for several weeks, was owing to the presence 

 of super-carbonate of lime, which came down with the rain. 



To prove what acid existed in the rain which fell during the 

 thunder-storm, the following tests were used : — 



A quantity of the infusion w'as boiled, and the colour became 

 considerably bluer. By adding a small quantity of lime-water to 

 the rain-water, a copious precipitate was produced. An inverted 

 receiver, filled with water over the shelf of a pneumatic trough, 

 had the beak of a retort introduced, which contained part of the 

 acidified rain-water ; a lamp was applied to the retort, and the 

 water made to boil, which caused a considerable quantity of gas to 

 be expelled ; and on introducing a lighted taper, it was imme- 

 diately extinguished. 



These experiments prove satisfactorily that the acid found in tlie 

 rain-water was the carbonic. 



The experiments have been many times repeated with similar 

 results. 



For what purposes in nature a substance which is known to be 

 destructive to animal life should accumulate to such an astonishing 

 degree, it is diflicult even to otter a conjecture. The formation of 

 carbonic acid from the lungs of animals, &c. is very great, as has 



* I helipvc it is not generally admitted that these gages exist in their separate 

 ilales 111 rhc alcno^iihere ; but surely, when we coii-.idfr (he peculiar nintioii of 

 iiipirors, the biuiultaacous occurrtucc of thunder, &c. there can be iio doubts oa 

 the nbjecl. 



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