11 



to Zonites cellarius, Zonites lucidus, and Zonites nitidulus, it was 

 not satisfactorily ascertained whether their heads were buried du- 

 ring the process of growth. 



. J. LOWE. 



Observatory, Beeston, 

 1854, February 14th. 



II. " Note on the Decomposition of Sulphuric Acid by Penta- 

 chloride of Phosphorus." By ALEXANDER WILLIAMSON, 

 Ph.D., F.C.S., Professor of Practical Chemistry in Univer- 

 sity College. Communicated by Dr. SHARPEY, Sec. U.S. 

 Received February 23, 1854. 



Chemists have long been aware of the fact that some acids unite 

 with bases in one proportion only, others in two or more proportions. 

 Thus a given quantity of nitric acid forms with what is termed its 

 equivalent of potash, a definite nitrate of potash ; if less than this 

 equivalent quantity of potash were added to the nitric acid, the 

 product would be a mechanical mixture of the same nitrate of potash 

 with uncombined nitric acid ; if more than the equivalent of potash 

 were added, the excess of alkali would remain uncombined. Sul- 

 phuric acid, on the other hand, is capable of forming two compounds 

 with potash, and it depends upon the proportions in which the two 

 substances are brought together whether the neutral or acid sulphate 

 is formed. 



The number of compounds which an acid forms with one base is 

 now considered as indicating its atomic weight. The weights of 

 sulphuric and nitric acids which are respectively susceptible of neu- 

 tralizing the same quantity of potash are termed equivalent, but 

 these are by no means the same as their atomic weights. Sixty- 

 three parts of nitric acid (nitrate of water) contains the same quantity 

 of hydrogen as forty-five parts of sulphuric acid, and when they are 

 neutralized by potash the whole of this hydrogen is removed and 

 replaced by potassium ; and if neither of the acids could combine in 

 any other proportion with potash, their atomic weights would be the 

 .. same as their equivalent weights. But sulphuric acid also forms a 

 potash compound in which half of its hydrogen is replaced by potas- 



