12 History of physical Science from [July, 



determinate weight and pressure, or rather to reduce these 

 operations to a single question of the rule-of-three. We refer 

 those who wish to provide themselves with such an instrument 

 to the Royal Institution Journal, v. 52. 



V. ACIBTFIABLE COMBUSTIBLES. 



1. Method of obtaining pure Hydrogen. — Hydrogen gas is 

 liable to be contaminated by certain impurities which exist in 

 metals, usually employed in preparing it. Hence I conceive the 

 reason why its specific gravity, as determined by direct experi- 

 ment, has always been considerably above the truth. Mr. 

 Donovan prepai-ed hydrogen gas from zinc and iron, acted on by 

 diluted sulphuric, and muriatic acid. By passing it through 

 caustic ammonia, he obtained traces of sulphureted hydrogen, 

 while lime water retained a small portion of sulphur. Hydrogen, 

 purified in this way, had exactly the smell of phosphorus, and 

 burned with a green flame. On the supposition that it might 

 contain phosphorus, it was made to pass through four Woulfe's 

 bottles. The first was filled with lime water, the second with 

 nitrous acid, the third with water, and the fourth with a solution 

 of sulphate of iron. Hydrogen gas, purified in this manner, had 

 no smell whatever, and gave so little light when burning, that 

 the colour of the flame could not be determined. — (Ann. de 

 Chim. et Phys. ii. 375.) 



2. SvJpkuret of Phosphorus. — It is well known that when 

 sulphur and phosphorus are heated together in a small glass 

 tube, they unite and form a compound, which varies in its 

 appearance according to the proportion of the two substances 

 employed, and which decomposes water at the ordinary temper- 

 ature of the atmosphere. Mr. Faraday found that when this 

 compound is shaken with ammonia, and left for a few hours in 

 that liquid, its impurities are removed, and a compound of a light 

 yellow colour, semitransparent, and more fluid, is obtained. It 

 may be kept in water without perceptibly acting on it. If sulphur 

 and phosphorus be added alternately to a portion of it, any 

 quantity of the two substances may be combined. A compound 

 prepared in this way, and containing about five parts of sulphur to 

 seven of phosphorus, didnotbecomesolidat20°, and was very fluid 

 at 32°. On remaining for some weeks in a bottle with water, it 

 deposited crystals of pure sulphur, and a compound remained 

 which was not so fusible as the former ; but on remaining in an 

 atmosphere of 38° or 40° for 12 or 14 hours, became a crystalline 

 mass. This Mr. Faraday considers as a definite compound of 

 sulphur and phosphorus. He attempted to analyse it, but did 

 not succeed very well. His result was sulphur, 4 ; and phos- 

 phorus, 8. He considers this as nearly one atom sulphur and 

 three atoms phosphorus ; but the weight of an atom of phos- 

 phorus exceeds his estimate. — (Royal Institution Journal, iv. 361.) 



3. C harry Substance found in a Porcelain Furnace. — This 



