594 Royal Irish Academy, 



"Fifth Experiment. — Five cylinders of zinc, 10 inches high, \ dia- 

 meter, were placed in glass vessels containing sulphuric acid, as be- 

 fore. Into these were placed cylindrical earthenware vessels, 1^ 

 inch diameter, containing pure nitric acid ; slips of platina foil were 

 rolled into cylinders as before. 



Cubic inches. 



Time, 2 minutes 20*0 



After 10 25-0 



After 30 . . . 30-0* 



" From these data may be calculated the heights of the zinc pipes, 

 and the weight of platina foil required to obtain any given decompo- 

 sition, to be employed, as shown by Jacobi, either as a motive power, 

 or applied to light-houses, to the polariscope, or to the fusion of re- 

 fractory substances. For the latter purposes, I had fixed to a strong 

 shallow woolf-bottle, two tubes with glass cocks, and to them tubes 

 containing chloride of calcium, applied to a Daniell's jet, playing upon 

 a cylinder of lime rotated by clockwork. A third tube was in- 

 serted in the bottle, intended as a regulation of the pressure, or a 

 safety-valve, in case of explosion." 



Dr. Apjohn then made a brief verbal communication on the sub- 

 ject of the composition of Pyrope. This mineral, long confounded 

 with garnet, is known to be distinguished from it by containing 

 chrome, and by exhibiting, not the dodecahedral, but the hexahedral 

 form. The best analyses of it, however, which are by Kobel and 

 Wachtmiester, are obviously imperfect, of which no better proof can 

 be given than that Gustavus Rose, in his Crystallography, does not 

 attempt to give the formula of the mineral, but contents himself with 

 enumerating the different oxides of which it is composed. Under 

 these circumstances, Dr. Apjohn conceived that a re-examination of 

 the constitution of pyrope would not be without interest. He there- 

 fore undertook its analysis ; and the result has been that he has 

 detected in it yttria, one of the rarest of the earths ; one, in fact, 

 which had previously been known to exist only in a few minerals 

 of exceeding scarcity. The yttria was insulated in the following 

 manner : — 



The mineral being fused with carbonate of potash, and the silex 

 separated in the usual way, the peroxide of iron, alumina, and yttria 

 were precipitated together by a mixed solution of ammonia and sal- 

 ammoniac. The alumina was taken up by caustic potash ; and to 

 the iron and yttria, dissolved in a minimum of muriatic acid, 

 such a quantity of tartaric acid was added, that upon subsequently 

 pouring in ammonia in excess there was no precipitate produced. 

 The iron was now removed by sulphuretted hydrogen ; and the 

 solution evaporated to dryness, and ignited in a large platinum 



* "The dilute acid in the voltameter began to boil; the cause of the in- 

 crease of decomposition, compared to what took place in the small cylin- 

 der, was the small stratum of sulphuric acid between the porous vessel and 

 the zinc. For a continuous action, the zinc pipes, sealed at one end and 

 amalgamated, should be connected, by pipes at top and bottom, with an 

 earthenware vessel containing the sulphuric acid." 



