Royal Society. 63 



{u 

 p, 46 4 . The analyses of these substances are 



given. 



When distilled in a pure state, the cerotic acid is volatile. When 

 mixed with other waxy matters, however, it passes by distillation 

 entirely into volatile oils, a circumstance which accounts for the fact 

 that it has never been found dissolved in the wax distillate. By 

 precipitating a weighed quantity of wax by acetate of lead, the 

 quantity per cent, of the cerotic acid in the bees'-wax, namely 22, 

 was determined. 



This acid was present in all the European bees'-wax examined by 

 the author ; but suspecting that its quantity might vary in other in- 

 stances, he procured bees'-wax from Ceylon, formed under different 

 conditions of climate and vegetation, and found on examination that 

 there was a total absence of the acid in that specimen. The author 

 draws attention to this curious variation in the nature of an animal 

 secretion under different conditions of life, a variation of which we 

 have another example in that of the volatile acid of butter, discovered 

 by Lerch* ; namely, that the butyric and caproic acid of one season 

 were, in another, replaced by vaccinic acid, differing from the former 

 acids in the amount of oxygen alone. 



" A statement of the working of the Compasses on board the 

 Honorable East India Company's Iron Steamer Pluto, from Septem- 

 ber 1841, on her passage from England to China, and during her 

 service in those seas, until her arrival at Calcutta in January 1S43." 

 By John Tudor, Commander It. N. Communicated by S. Hunter 

 Christie, Esq., Sec. R.S., &c. 



The author states that the compasses of the Pluto were adjusted 

 by Mr. Sims, of the firm of Troughton and Sims, by order of Mr. 

 Pencoote of the East India House, under whose directions that ship 

 was fitted out : and it is to the great pains taken by Mr. Sims in 

 placing the magnets employed for counteracting the local attraction 

 that the author attributes the undeviating accuracy of those com- 

 passes during the whole time the Pluto was under his command in 

 both hemispheres. He observes that, in the first place, much care is 

 required in securing the magnets, and protecting them from wet, 

 after their proper position has been ascertained. In the case of the 

 Pluto, two magnets were placed under the deck in the author's cabin ; 

 one of them eighteen inches below the deck, being, it is true, an eye- 

 sore, but one of trifling consideration, when compared with the great 

 importance of the well-working of the compass. The next point to 

 be attended to is that the cards, or needles, should be all of the same 

 size, and exactly corresponding with that of the compass used at the 

 placing of the magnets for counteracting the local attraction. The 

 bittacles should all be of the same make and height, and the compass- 

 boxes of the same size ; so that whenever a new compass or a fresh 

 bittacle is wanted, the circle in which the needle moves may remain 

 at the same angle from the magnet as at the first adjustment. On 

 a strict attention to these precautions will depend the well-working 

 of the compass in all iron vessels, and also in wooden vessels when- 

 * [Chem. Gazette, vol. ii. p. 377-] 



