166 A Tribute to the Memory of [Sept 



and I wish to produce all the evidence I can come at on both 

 sides. The other experiments are very curious, and will give 

 much satisfaction."* The investigation was afterwards resumed 

 by Mr. Henry, and made the subject of a paper, which is printed 

 in the second volume of the Memoirs of this Society. The 

 simplicity of the apparatus required for the performance of these 

 experiments has induced the authors of our best work on educa- 

 tion to point them out among others as calculated to please 

 young persons, and to gratify in them an enlightened curiosity 

 respecting the causes of natural phenomena.-t 



The occasion of Mr. Henry's next appearance as the author of 

 a separate work arose out of an accidental circumstance. He 

 had found that the water of a large still tub was preserved sweet 

 for several months by impregnating it with lime, though, without 

 this precaution, it soon became extremely putrid. This fact 

 suggested to him an eligible method of preserving water at sea;j: 

 but as lime water is unfit for almost every culinary purpose, 

 some simple and practicable method was required of separating 

 that earth from the water before being applied to use. This, he 

 ascertained, might be accomplished, at little expense, by car- 

 bonic acid, the gas from a pound of chalk and 12 ounces of oil 

 of vitriol being found sufficient for the decomposition of 120 

 gallons of lime water.§ The only difficulty was in the mode of 

 applying the gas on a large scale ; but this was overcome by the 

 contrivance of an apparatus, which Mr. Hemy described in a 

 pamphlet dedicated to the Lords of the Admiralty. The proposal, 

 in consequence of the zealous personal exertions of Mr. Wedg- 

 wood, who was then in London, met with due attention from the 

 Commissioners for victualling his Majesty's ships. The chief 

 obstacle to its adoption in the navy was an apprehension, proba- 

 bly well grounded, that persons would scarcely be found on ship- 

 board possessing sufficient skill for conducting the process 

 successfully. Since that time, the preservation of water at sea 

 has been accomplished by the simple expedient of stowing it in 

 vessels constructed or lined with some substance, which is not 

 capable of impregnating water with any putrescible ingredient ; 

 for good spring water, it is well known, contains essentially 

 nothing that disposes it to putrefaction. 



The philosophical pursuits of Mr. Henry, not long after this 

 period, received an additional stimulus by the establishment of 

 the Society to which these pages are addressed, and by his 



» Letler from Dr. Priestley to Mr. Henry, dated Jan. 5, 1777. 



+ Edgeworlh on Practical Education, vol. i. chap. 1. 



J Dr. Alston, of Edinburgh, appears, however, to have been the first who pro- 

 posed impregnation with lime, as a mean of preventing the putrefaction of water; 

 and to precipitate the lime, he suggested the use of carbonate of magnesia. 



<j The water, however, for which these proportions were sufficient, could not 

 have been completely charged with lime, for fully saturated lime water would have 

 required for decomposition nearly three times that quantity of chalk and oil of 

 vitriol. 



