TEST FOR CHLORINE.
The fifth tube we will examine for common salt, which is nearly always present in water. This test is done by dropping in some nitrate of silver solution, which produces a white precipitate, caused by the silver combining with the chlorine, which is the principal element in common salt. This is an excessively fine test, and the nitrate of silver will detect an incredibly small trace of common salt in water. The worst effect that common salt has in water, is to cause priming. Where it is present to any great extent, the blow-off cock should be used frequently on the road; and a surface-cock is quite an aid in keeping the boiler in order. Water that is taken from wells or streams about cities, and found to give strong chlorine re-actions, is nearly always contaminated with sewage.