-1859] WRITINGS OF JOSEPH HENRY. 173 



4th. The use of disinfectants, though perhaps less energetic 

 in destroying miasma than in decomposing odors, should 

 not be entirely neglected; and for this purpose a small quan- 

 tity of chloride of lime may be found beneficial. It is said 

 that the flashing of gunpowder in a room answers the same 

 purpose. 



5th. Screens of trees should be planted to interrupt the 

 dump and warm wind from the focus of the emanation. 



6th. During warm weather, when ventilation is more nec- 

 essary, the doors and windows should be provided with 

 screens of fine gauze. 



7th. Boiled water should be used in preference to any 

 other, or pure rain water, or that which has fallen some time 

 after the rain commences, to which add a small portion of 

 vinegar or acetic acid. 



8th. In cool evenings of summer, the dampness of the 

 house should be dissipated by a blazing fire upon the hearth. 



It appears that the malarious influence is produced at a 

 certain temperature, and that it is favored in marshy places 

 by the heating of the water in shallow pools. It has been 

 recommended to divide such places by deep parallel ditches 

 or narrow canals at right angles to the direction of the pre- 

 vailing wind, the earth being thrown up on the side in the 

 form of dykes, which are to be planted with rapidly growing 

 trees or large shrubs. The ditch collects the water in too 

 large bodies to be much heated, and this liability to become 

 warmed is further lessened by the shade of the trees. The 

 latter also serve as a series of screens to intercept any malaria 

 which may arise. 



Nitric Acid. — If sparks of electricity are passed through a 

 tube containing atmospheric air, the oxygen and nitrogen, 

 which do not combine under ordinary circumstances, will 

 chemically unite and form nitric acid. This union is sup- 

 posed to be the result of the production of ozonized oxygen, 

 which promply unites with the nitrogen on account of its 

 increased combining energy. The nitric acid thus formed 

 combines with ammonia, which is also found in the atmos- 

 phere as an original though a variable constituent, and forms 



