Sanitary engineering : a series of lectures given before the School of military engineering at Chatham, 1876 / by J. Bailey Denton.

  • John Bailey Denton
Date:
1877
Catalogue details

Licence: Public Domain Mark

Credit: Sanitary engineering : a series of lectures given before the School of military engineering at Chatham, 1876 / by J. Bailey Denton. Source: Wellcome Collection.

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    APPENDIX G. THE SOFTENING OF WATER BY LIME. [Extracted from the Sixth Report of the Rivers Pollution Commissioners,'] The economy which carbonate of soda exhibits in comparison with soap, as a softening agent, is far surpassed by the gain which results from the use of lime for this purpose. The latter material costs only about 8d. per cwt., and this weight of lime will do the work of 20|- cwts. of soap in softening hard water. To soften a quantity of hard water which requires one cwt. of lime the following would be the weight and cost of the three alternative materials :— £ s. d. 1 cwt. quicklime ... ... ... 00 8 4| cwts. carbonate of soda ... ... 217 9 20J cwts. soap ... ... ... ... 47 1 8 There is thus an enormous economy in the use of lime, and in the discovery of this process the late Dr. Clark, Professor of Chemistry in the University of Aberdeen, conferred a valuable boon upon the inhabitants of many hard-water districts. Dr. Clark's patent right has expired, and the public are therefore free to use this cheap and simple method of rendering hard water suitable for washing and cleansing purposes. The process is, however, only applicable to water which owes its hardness, entirely or chiefly, to the carbonates of lime and magnesia (temporary hardness). Water which is hardened by sulphate of lime or sulphate of magnesia (permanent hardness), cannot be thus softened, but any water which softens by boiling for half an hour will be softened to an equal extent by this method. The hard water derived from chalk, limestone, or oolite districts is generally well adapted for it. The following is Dr. Clark's own account of the process (Journal of the Society of Arts, 16th May, 1856) :— ' In order to explain how the invention operates, it will be neces- sary to glance at the chemical composition and some of the chemical properties of chalk; for, while chalk makes up the great bulk of the matter to be separated, chalk also contains the ingredient that