no THE POPULAR SCIENCE MONTHLY. 



rapid rinse with water containing a few drops of vinegar will 

 neutralize the free alkali and prevent much of the mischief. 



We have now dealt with our grease solvents and dirt looseners, 

 but without the aid of water they would be useless ; and experi- 

 ence teaches us that the source of the water used for cleansing 

 has a great deal to do with its efficiency. 



As the newborn raindrops fall from the breaking clouds, they 

 are practically pure water, containing at most traces of gaseous 

 impurities which the mist has dissolved from the upper strata of 

 air while journeying in the form of cloud, and where the rain is 

 collected in the open country, it gives us the purest form of natu- 

 ral water healthful to drink, because it is highly aerated, and free 

 from all impurity, organic and inorganic, and delightful to wash 

 in because of its softness and the ease with which the soap gives 

 a lather. 



In towns, however, a very different state of things exists, as 

 the rain in falling washes the air from a large proportion of the 

 suspended organic matters inseparable from a crowded city, and 

 also from the unburned particles of carbon, which incomplete 

 combustion allows to escape from our chimneys; and charged 

 with these, it still collects more dirt of various kinds from the 

 roofs of our houses, and finally finds its way into our water-butts 

 as the semiputrid sludge which often causes the true-bred cock- 

 ney to wonder " if this so-called purest form of natural water is 

 so foul, what on earth must the other forms of water be like ? " 

 If in the country the rain water is collected and stored in suitable 

 reservoirs, then we have the most perfect water that can be ob- 

 tained for washing and cleansing purposes. 



In the passage of the rain through the air small quantities of 

 carbon dioxide or carbonic-acid gas are dissolved from the atmos- 

 phere, while in slowly percolating through the surface soil on 

 which it has fallen the water is brought in contact in the pores of 

 the soil with far larger volumes of this gas, which is being con- 

 tinually generated there by the decomposing vegetation and other 

 organic matter in a state of decay. Under these circumstances 

 the water becomes highly charged with the gas, and sinks on 

 through the ground until it comes in contact with some imper- 

 meable strata through which it can not penetrate, and here it col- 

 lects until a sufficient head of water has been formed for it to 

 force its way along the strata to the surface of the earth, where it 

 now appears as a spring, and during this passage through the 

 earth it has dissolved everything that will yield to its own solvent 

 action or to the activity of the carbon dioxide, which dissolved in 

 water forms the weak carbonic acid, a compound which will dis- 

 solve many substances insoluble in the water itself, such as calcic 

 carbonate, occurring in the soil as marble, limestone, or chalk. 



