Professor FRANKLAND has considered it important to investigate the conditions under which the germs pass from sewage into the air. Does the flow of sewage in a properly-constructed sewer produce sufficient agitation to disperse liquid particles through the air space of the sewer? In this and in the other experiments mentioned below a solution of lithic chloride was used,
Professor FRANKLAND having previously ascertained by three separate tests that no lithic chloride is carried off at ordinary temperatures by aqueous vapour from a saturated solution of it. Some of the solution being placed in a glass jar it was agitated, and though this was done with greater violence than would ever happen to fluid in a sewer, it was proved that none of the lithic chloride was disengaged. It is, therefore, extremely improbable that the mere flow of foul liquid through sewers can impregnate the circumambient air with suspended particles. There is, however, another kind of agitation to which sewage is subject that may produce a very different result -- viz., the development of gases during the processes of fermentation and putrefaction. When minute bubbles burst at the surface of an effervescing liquid little particles of it can be seen projecting into the air some inches, and then falling again. Professor FRANKLAND experimented to test whether particles too small to be seen might not be also projected, and in consequence of the smallness of their masses in relation to their sectional areas, might continue suspended in the air for a long time.
A strong solution of lithic chloride was acidulated by the addition of hydrochloric acid, some fragments of white marble were added, and this produced an effervescing liquid. A tube 3in. in diameter and 5ft. long, was held over it, and there were distinct traces of lithium found during effervescence at the upper end. A second 3in. in diameter and 12ft. long, was then held nearly at right angles at the top of the first, a slight draught through it being caused by external heating. At the further end of this tube, too, lithium was distinctly traced.
The particles were also found to pass readily through two inches of charcoal, and they passed even a layer five inches thick, though in greatly diminished numbers. Here then in the breaking up of minute gas bubbles is a cause of the suspension of particles in the air. If, therefore, through the stagnation of sewage or constructive defects which allowed of the retention of excrementitious matters for several days in a sewer, putrefaction set in, then gases are generated, ant the dispersion into the air of zymotic matters is very probable. It is of the greatest importance that foul liquids should pass rapidly and freely through drained pipes and sewers, so as to secure their discharge from the system before putrefaction sets in.