104 On the Liquefaction and Solidification [1844. 



comes a clear liquid, and this point is close upon that which 

 corresponds to a vaporous pressure of one atmosphere. The 

 acid dissolves the cap cement and the bitumen of the gauge 

 graduation ; and appears also to dissolve and act on fat, for it 

 leaked by the plug of the stopcock with remarkable facility. 

 It acts on the brass of the apparatus, and also on the mercury 

 in the gauge. Hence the following results as to pressures and 

 temperatures are not to be considered more than approxi- 

 mations : 



At Fahr. pressure was 2*90 atmospheres. 



At 32 Fahr. pressure was 3*97 atmospheres. 



At 60 Fahr. pressure was 5*86 atmospheres. 



Hydrobromic Acid. This acid was prepared by adding to 

 perbromide of phosphorus* about one-third of its bulk of water 

 in a proper distillatory apparatus formed of glass tube, and then 

 applying heat to distil off the gaseous acid. This being sent 

 into a very cold receiver, was condensed into a liquid, which 

 being rectified by a second distillation, was then experimented 

 with. 



Hydrobromic acid condenses into a clear colourless liquid at 

 100 below 0, or lower, and has not the pressure of one atmo- 

 sphere at the temperature of the carbonic acid bath in air. It 

 soon obstructs and renders the motion of the mercury in the 

 air-gauge irregular, so that I did not obtain a measure of its 

 elastic force; but it is less than that of muriatic acid. At and 

 below the temperature of 124 Fahr. it is a solid, transparent, 

 crystalline body. It does not freeze until reduced much lower 

 than this temperature ; but being frozen by the carbonic acid 

 bath in vacua, it remains a solid until the temperature in rising 

 attains to 124. 



Fluosilicon. I found that this substance in the gaseous 

 state might be brought in contact with the oil and metal of the 

 pumps, without causing injury to them, for a time sufficiently 



* The bromides of phosphorus are easily made without risk of explosion. 

 If a glass tube be bent so as to have two depressions, phosphorus placed in 

 one and bromine in the other ; then by inclining the tube, the vapour of bro- 

 mine can be made to flow gradually on to, and combine with, the phosphorus. 

 The fluid protobromide is first formed, and this is afterwards converted into 

 solid perbromide. The excess of bromine may be dissipated by the careful 

 application of heat. 



