290 Messrs. E. T. Chapman and M. H. Smith on the 



in the following terms. Some evidence has been brought for- 

 ward to show : — 



(1) That by an alteration in the construction of formulae, the 

 atomic ratios of the silicates may be easily expressed in accord- 

 ance with the principles of modern chemistry, while some prac- 

 tical advantages are gained, and those attending the use of the 

 old formula? are retained. 



(2) That the constitution and relations of the silicic hydrates 

 and salts are best understood by regarding them as (a) containing 

 the elements of the primary SiO 2 , or (b) a polymer of this. 



(3) That the rate of condensation of SiO 2 within the mole- 

 cule of a native anhydrous salt is represented by the number 3, 

 or a multiple of this by 2 or 3 only =Si0 2 , SiO 6 , 2 SiO 6 , 3 SiO 6 ; 

 that this alteration can take place without interfering with the 

 general type of the compound, and that, the passage from one 

 stage of accumulation to another can be easily explained by re- 

 ference to the known properties of normal and polysilicic hy- 

 drates. 



It is also shown that the silica, hitherto regarded either as 

 basic or as accessory in such minerals as the felspars, is present 

 really as the result of the partial or complete satisfaction of the 

 tendency of SiO 6 to pass successively into 2 SiO 6 and 3 SiO 6 , the 

 chemical conditions of the mass in which the mineral may have 

 been formed determining the degree of condensation within the 

 molecule. 



XXXVII. Limited Oxidation of Ethyl-crotonic Acid. 

 By Ernest Theophron Chapman and Miles H. Smith*. 



THE ethyl-crotonic acid employed in the following experi- 

 ments was prepared from diethoxalate of ethyl in the 

 manner described by Frankland and Duppa. The process con- 

 sists in adding trichloride of phosphorus to the diethoxalic 

 ether f. The ether loses one atom of water, thus : — 

 Diethoxalic ether. Ethyl-crotonic ether. 



, jl 



fC(C 2 IP) 2 OH cp _ rC(C 2 H 4 )C 2 H* , PH 3 3 + 3HC1 

 d \CO(C 2 H 5 )0 +i bl ~ d \CO(C 2 H 5 )0 +i ^ U + dHU 



At the same time red amorphous phosphorus is deposited. This, 

 we suppose, owes its origin to an action between the phosphorous 



* Communicated by the Authors. 



f For the preparation of this ether see " Synthetical Researches on Acids 

 of the Lactic Series/' by Frankland and Duppa, Phil. Trans, for 1866, 

 p. 309; and also Journal of the Chemical Society, April 1867, where an 

 improved method of preparing the ether is described by us. 



