378 Analyses of Books. [Nov. 



Article IX. 



Analyses of Books. 



Transactions of the Royal Society of Edinburgh, Vol. VIII. 



Part II. 1818. 



This part contains the following papers : 



I. On the Effects of Compression and Dilatation in altering the 

 Polarizing Structure of Doubly Refracting Crystals. By David 

 Brewster, LL.D. F.R.S. Lond. and Edin. — Dr. Brewster shows 

 that when pressure is applied to a thin plate of calcareous spar 

 bounded by planes perpendicular to the axis of double refraction 

 (the shorter diagonal of the crystal), the circular rings of colour 

 formerly observed change their shape. A similar effect is pro- 

 duced upon quartz, and indeed upon all doubly refracting crystals, 

 whether negative or positive. He shows very ingeniously that 

 this alteration is not owing to a modification of the original 

 force, but to the creation of a new force. Hence it is easy to 

 determine a priori the effect of compression or dilatation upon 

 doubly refracting crystals. When positive crystals are com- 

 pressed parallel to the axis of the crystal, the tints rise ; when 

 the axis of compression is perpendicular to the axis of the crystal 

 the tints descend. When the same crystals are dilated, the 

 opposite effect takes place. If the crystals be negative, compres- 

 sion in the direction of the axis makes the tints descend ; perpen- 

 dicular to the axis, it makes them rise. By dilatation, vice versa. 



II. Experiments on Muriatic Acid Gas, with Observations on 

 its Chemical Constitution, and on some other Subjects of Che- 

 mical Theory. By John Murray, M.D. F.R.S.E. This paper 

 will be printed in a future number of the Annals. 



III. Experiments on the Relation between Muriatic Acid and 

 Chlorine; to which is subjoined the Deseription of a new Instru- 

 ment for the Analysis of Gases by Explosion. By Andrew Ure, 

 M.D. Professor of the Andersonian Institution, and Member of 

 the Geological Society. 



It has been demonstrated by decisive experiments, and is 

 uin .eisally admitted, that when chlorine and hydrogen gases are 

 mixed together in equal volumes, and an electrical spark is passed 

 through the mixture, these two gases disappear, and there is 

 found in place of them a quantity of dry muriatic acid exactly 

 equal in volume to the two gases before the combustion. Two 

 explanations of this fact have been advanced. Gay-Lussac and 

 Thenard, who, as far as I know, were the first chemists that 

 established the fact by rigid ' experiments, explained it in this 

 way. Chlorine gas is a compound of one volume of muriatic 

 acid and half a volume of oxygen condensed into one volume. 

 The volume of hydrogen combines during the combustion with 

 the half volume of oxygen, and forms water. This water unites 

 with the muriatic acid, which is incapable of existing without it 



