Mr. R. Phillips on the Use of Chemical Symbols. 443 



of the posterior legs are destitute of spines, but the tarsi have some minute 

 black ones on their exterior side, and the terminal joint has a longitudinal 

 row of long, closely set, slender spines or bristles on the inferior part of 

 its inner surface. Each tarsus is terminated by three black claws ; the two 

 superior ones are much curved (the one on the anterior side being the 

 larger) and have a single large tooth near the base; the inferior claw is 

 small and bent abruptly downwards. The palpi, which are long and pe- 

 diform, are inserted at the anterior extremity of the maxillae ; the second 

 joint is greatly compressed, and curved ; the ultimate and penultimate 

 joints are supplied with numerous short, strong, black spines on their sides, 

 the former having a large black claw at its termination, which is provided 

 with a solitary tooth near its base. All these parts, with the preceding ex- 

 ceptions, are of a deep red-brown colour, the mandibles and the depressed 

 part of the tibiae of the third pair of legs being the darkest. The abdo- 

 men is somewhat oval, and of a yellowish brown colour; its posterior ex- 

 tremity presents four spinning mammillae ; the two superior ones are ro- 

 bust, and prominent, each consisting of three joints, and the two inferior 

 ones are minute. In this species the papillae from which the silk issues 

 occupy a circular space at the extremity of each mammula. 



Length, from the most prominent part of the mandibles to the ex- 

 tremity of the abdomen, not including the spinners, 1 inch and ■&&» ; 

 length, from the anterior margin of the cephalothorax to the extremity of 

 the abdomen, 1-^V; length of the cephalothorax ■$■; breadth f; length of 

 a posterior leg 1^; length of a leg of the third pair -£j-; length of a su- 

 perior spinning mammula \. 



LXXI. Observations on the Use of Chemical Symbols. By 



R. Phillips, F.R.S. 8?c. 

 /CHEMICAL symbols have for several years been very 

 ^-^ generally in use on the Continent, and the employment of 

 them is now rapidly extending in this country. At first they 

 seem to have been chiefly intended as brief representations 

 of accompanying detailed statements, and even this purpose 

 they sometimes failed to answer. Now, however, symbols are 

 given without the composition of bodies, and even without their 

 atomic weights. The inconvenience arising from this prac- 

 tice I have frequently experienced, and on no occasion more 

 sensibly than in perusing Mr. Graham's paper in the forth- 

 coming Part of the Philosophical Transactions, entitled, Re- 

 searches on the Arseniates, Phosphates, and Modifications of 

 Phosphoric Acid. I intend, on a future occasion, to give a full 

 account of the important conclusions which the author has 

 deduced from his experiments*, when, by the assistance which 

 I hope to receive from him, he has rendered the details of his 

 paper intelligible, by explaining the symbols employed in it. 

 In order to put Mr. Graham in possession of the difficulties 

 which have occurred to me, and which must, I think, have 



* An abstract of Mr. Graham's paper will be found in our present Num- 

 ber, pp. 451, 452. 



3 L2 



