A. Because it always takes in its course the _best conductors_; and will fly both right and left, in order to reach them. Q. _Why does LIGHTNING turn MILK SOUR?_ A. Lightning causes the gases of the air (through which it passes) to _combine_, and thus produces a poison, called _nitric acid_; some small portion of which, mixing with the milk, turns it sour.[2] (N. B. Sometimes, the mere _heat_ of the air, during the storm, turns milk sour.) [2] The air is composed of two gases, called oxygen and hydrogen, _mixed_ together, but _not combined_. If oxygen is _combined_ with nitrogen, it produces five deadly poisons, viz.--nitrous oxide, nitric oxide, hyponitrous acid, nitrous acid, and nitric acid, according to the proportion of each gas in the combination. Q. _What is the difference between COMBINING and MIXING?_ A. When different ingredients mingle _without undergoing any chemical change_, they are said to be _mixed_; but when the natural properties of each are _altered by the union_, then those ingredients are said to be _combined_. Q. _Give me an example._ A. If different coloured sands be shaken together in a bottle, the various grains will _mix_ together, but not combine: but if water be poured on quick lime, the water will _combine_ with the lime, and not mix with it. Q. _Why are the different grains of sand said to be MIXED, when they are shaken together?_ A. Because they are mingled together, but the property of each grain remains the _same as it was before_. Q. _Why is water poured on lime, said to COMBINE with it?_ A. Because the properties, both of the water and the lime, are _altered_ by the mixture: the lime alters the character of the water, and the water alters the character of the lime. Q. _Do oxygen and nitrogen COMBINE, or only MIX together, in common atmospheric air?_ A. They only _mix_ together, as grains of sand would do, when shaken in a bottle. When oxygen and nitrogen _combine_, they do not constitute _air_, but acid _poisons_. Q. _Why does LIGHTNING turn BEER SOUR, although contained in a close cask?_ A. If the beer be _new_, and the process of fermentation not complete, lightning will so _accelerate_ the process, as to turn the liquor sour. Q. _Why is NOT old beer and strong PORTER made SOUR by lightning?_ A. Because the _fermentation is complete_ already; and, therefore, is not affected by electrical influence. Q. _Why is METAL sometimes FUSED by lightning?_ A. Because the dimension of the metal is _too small_, to afford a path for the electric current. Q. _Why does LIGHTNING PURIFY the AIR?_ A. For two reasons: 1st--Because the oxygen and nitrogen of the air _combine_,[3] and produce "nitric acid:" 2ndly--Because the agitation of the storm _stirs up the air_. [3] The oxygen and hydrogen are not _combined_, but simply _mixed_ in the ordinary air; but the lightning causes the mixed elements to _combine_. Q. _How does the production of nitric acid purify the air?_