( 90 ) 

 which chiefly constitute the fetid gasesarising 

 from privies. 



To absorb and neutralize these vapors, re- 

 course must be had to neutral or only slightly 

 acid metallic salts, of which, the cheapest and 

 most abundant is the sulphate of the protoxide 

 of iron or common green vitriol of the shops. 

 (If it should be too acid, neutrality can be 

 readily obtained, by adding, to the solution of 

 the salt, a little quick or slacked lime in pow- 

 der.) In fact a double decomposition ensues, 

 producing sulphate of ammonia and sulphuret 

 and carbonate of iron. A certain proportion 

 of plaster (sulphate of lime,) may be added to 

 the sulphate of iron ; it decomposes the car- 

 bonate of ammonia more readily and com- 

 pletely than the hydrosulphate ; a little char- 

 coal dust is also an useful addition for the ab- 

 sorption of the other peculiar odors (inde- 

 pendent of the volatile ammoniacal salts,) 

 which are emitted. 



This mixture can be applied to the sinks, 

 either in dry powder or thinned with water. 

 Perhaps it is preferable to use it in solution, 

 the soluble portion by all means, for more or 

 less of the powder reaches the bottom of the 

 sink before being dissolved, and hence a par- 



