373 



SCIENTIFIC RECREATIONS. 



it burns in, and is very trying to the eyes, as well as destructive to gilt 

 ornaments. 



Tar is familiar to all readers, and though unpleasant to handle or to 

 smell, it produces the beautiful aniline dyes. Tar pills are very efficacious 

 for some blood disorders, and will remove pimples, etc., from the face, and 

 cure " boils " effectually. If a dose of five be taken first, in a day or two 

 four, and so on, no second remedy need be applied. We have known cases 

 finally cured, and no recurrence of boils ever ensued after this simple 

 remedy. 



Tar is one of the results left in the distillation both of wood and coal : 

 in places where wood is plentiful and tar in request, it is produced by 

 burning the wood for that purpose ; and in some of the pits in which char- 

 coal is produced, an arrangement is made to collect the tar also. Coal-tar 



. 381. Tar manufactory 



and wood-tar are different in some respects, and are both distilled to procure 

 the napthas which bear their respective names. From wood-tar creosote is 

 also extracted, and it is this substance which gives the peculiar tarry 

 flavours to provisions, such as ham, bacon, or herrings, cured or preserved by 

 being smoked over wood fires. Tar is used as a sort of paint for covering 

 wood-work and cordage when much exposed to wet, which it resists better 

 than anything else at the same price ; but the tar chiefly used for these 

 purposes is that produced by burning fir or deal wood and condensing the 

 tar in a pit below the stack of wood ; it is called Stockholm tar, as it comes 

 chiefly from that place. 



Carbon only combines with nitrogen under peculiar circumstances. 

 This indirect combination is termed cyanogen (CN). It was discovered by 

 Gay-Lussac, and is used for the production of Prussian blue. Hydro- 

 cyanide of potassium (Prussic acid) is prepared by heating cyanide of 



