George Frederic Barker. '227 



after which the boihng was continued for eight or ten minutes, 

 the liquid allowed to cool, and then filtered. A second portion 

 of the original silver solution was treated with ammonium 

 hydroxide until the precipitate formed was almost redissolved, 

 after which water was added and the liquid filtered. To silver 

 glass, equal portions of these two fluids, thoroughly mixed, 

 were poured upon it. After a lapse of about ten minutes, a 

 brilliant layer of metallic silver was deposited. By repeating 

 the process the layer could be thickened to any desired extent. 

 A somewhat earlier article is entitled "Account of the Casting 

 of a Gigantic (Rodman) Gun at Fort Pitt Foundry " (ibid., 

 xxxvii, 296) ; this contains some important practical sug- 

 gestions. 



An interesting contribution is made by Dr. Barker, in the 

 same Journal ( (2), xliv, 203, 1867), in support of the view that 

 formic acid is carbonous acid. He believed this to be true 

 because of the ready formation of formic acid by the partial 

 oxidation of carbon, and also because it resulted from the 

 oxidation of carbonic acid. For these reasons he further con- 

 cluded that formic acid was the acid of bivalent carbon. 



In an extended communication " On Normal and Derived 

 Acids," (ibid., xliv, 384), he arrived at the following con- 

 clusions : 



"1. That all the bonds of any simple radical may be saturated 

 by the monad hydryl (OH). 2. That the compounds this 

 formed, being evidently normal, are conveniently designated by 

 the prefix orlho. 3. That the equivalence of negative radicals 

 varies through several stages, while that of positive rarely 

 changes, and hence, that there may be a series of ortho-acids from 

 a given negative radical, but only a single base from a positive 

 one. 4. That by the removal of the elements of water from a 

 normal or ortho-acid, a derived acid is produced, which may be 

 indicated by the prefix meta. 5. That wlien there are several 

 such derivatives, the Greek numeral prefixes di, tri, tetra, etc., may 

 be used to indicate the number of molecules of water removed 

 from the ortho-acid to yield the meta-form. 6. That interme- 

 diate between the simple ortho- and the meta-acids are others 

 containing more than a single atom of the negative radical ; and 

 that these acids may be designated bj^ di, tri, tetra, etc. (accord- 

 ing to the number of negative atoms) prefixed to the name of 

 the acid, while the number of molecules of water removed from 

 a multiple of the normal acid to form them is indicated by the 

 same numerals prefixed to the meta. 7. That while the negative 

 atoms in the compounds just mentioned are united by oxygen, 

 there may be other compounds whose negative or positive atoms 

 are united dii'ectly ; thus producing a fourth class of acids and 

 of bases. 



