q6 philosophical transactioxs. [anno 1776. 



of vapour, and, there decomposing the empyreumatic oil, produces heat and 

 bkie Hght ; the stratum of vapour, within the outer burning surface, is heated 

 white-hot; the heat diminishes towards the centre, which, if the flame be large, 

 is scarcely red-hot ; as the column rises, decomposition taking place constantly 

 on its surface, it necessarily diminishes, and the upper part of the flame is 

 conical. That the tallow boils in the wick can be seen : that it is converted into 

 empyreumatic oil is proved by drawing the vapour, rising in the middle of the 

 flame, where it does not burn, into a glass tube ; the empyreumatic oil con- 

 denses. This also shows that the flame does not burn in the middle. That the 

 heat is produced on the outer surface appears, if we take a small rod of glass, 

 and put the end of it in the blue flame on the surface ; it will be heated white- 

 hot and melt. Immerse the rod into the flame, so that the point shall be in 

 the centre, it will melt and bend where it is in the blue flame on the surface ; 

 whereas, if the flame be large, the point which is in the centre will hardly be 

 heated red-hot. That the empyreumatic oil is decomposed, is proved by burning 

 a candle with a very small wick in distilling vessels, no condensation of empy- 

 reumatic oil takes place. We may conclude therefore that light is produced by 

 the decomposition, as well as by the ignition, in inflammation. 



Lest the manner of powdering phosphorus should not be known, Dr. F. gives 

 the process : take phosphorus of urine 2 drs. ; put it into a 4 oz. phial ; pour on 

 it 3 oz. of water ; heat it gently, by immersion in warm water, till the phos- 

 phorus melts ; shut the phial with a cork ; take it out of the water, and shake 

 it briskly till it be cold ; the phosphorus will be found in powder. 



XXXI. Experiments on Ignited Bodies. By J. Roebuck, M. D., F. K. S. p. 50Q. 



Mr. Buftbn asserts, that he found a ball of iron, which weighed 49 lbs. goz. 

 when cold, to weigh, when heated to a white heat, 49 lbs. 11 oz. which is an 

 augmentation of weight of I9-I- grains to the pound. This extraordinary fact, 

 circumstantially narrated by that ingenious author, being contrary to the opinions 

 of those philosophers who have most enlarged our natural knowledge by their 

 candid and cautious inquiry into the qualities of bodies, induced Dr. R. to make 

 similar experiments. 



Some time ago, when at Birmingham, he had very luckily an opportunity, 

 oy the aid of two accurate balances of Mr. Bolton's ; one of which would, 

 without straining the beam, weigh a pound and turn with the 10th of a grain ; 

 and the other weigh half an ounce, and turn with the 100th part of a grain. 

 Dr. R. heated a piece of iron, of nearly 1 lb, weight, to a white heat, or what 

 the smiths call a welding heat, and found, by the most accurate experiments he 

 could make, and several times repeated, that the iron, when left se\eral hours in 

 the balance to cool, weighed nearly one grain less when cold than w hen hot ; 



