382 PROCEEDINGS OF THE AMERICAN ACADEMY 



" Another point observed in the decomposition of olefiant gas de- 

 serves notice. It is stated in most treatises on chemistry, and adopted 

 as a. matter of belief in the gas manufacture, that olefiant gas, when 

 heated, deposits two of its four proportions of carbon, and, without 

 change of volume, becomes marsh gas. It is barely possible, as an 

 accidental circumstance, this proportion of carbon might be deposited, 

 but it would take place, not as an experimental, but as a chance re- 

 sult. When olefiant gas is passed through ignited quartz, glass, or 

 iron-turnings, it deposits carbon, which has no definite relation to the 

 composition of the gas., a mixed gas being left, containing olefiant 

 marsh gas and hydrogen. If the gas is repassed, the carbon may be 

 nearly all abstracted. +^~ marsh gas suffering decomposition. 



" The conditions of olefiant gas heated in the products of coal de- 

 composition are not such as to lead to a breaking up of its carbon 

 arrangement, for there are many reasons for the statement, that this 

 bicarburet is itself the result of change in the vapor of paraffine and 

 other hydrocarbons of the oily characters. 



" It seems, therefore, a correct deduction from observation and ex- 

 periment, that gas-carbon is not produced from olefiant gas by depo- 

 sition, but is a product of changes caused by heat in vapors of hydro- 

 carbons, and that this allotropic carbon, in other cases, forms in the 

 presence of vapors, which can transport carbon in the vesicular 

 state." 



Dr. Pickering referred to his having stated in print, that 

 Manetho has given two distinct dates for the Fall of Troy : 

 one of them (counting downwards in the Africano-Manetho 

 Table) = B. C. 1127; and the other (in the Fragments pre- 

 served by Josephus, completed from the first-named source) 

 = B. C. 1072. The earlier, being a Greek date, had always 

 appeared doubtful, from the fact that Manetho was writing 

 for a Greek Emperor. Since the publication of the above 

 statement, Dr. Pickering has found that the Africano-Manetho 

 Table contains both dates; the lower one in the Dynastic 

 numbers, which (counted upwards from " B. C. 339," the ad- 

 justment supplied by Syncellus) give, 



" 9 4- 38 + 20^ + 6 +124^ -f 150^. -f 40+6 +89 +120 +130 " 



= B. C. 1072^. 



