TllANSACTIONS OF SECTION A. 



6.33 



.strong:, tlif effert nf (lie dt'sct'tnlinp ciirrcnt was to promolo tlic tliimiin^' of the 

 tiliii. An asct'iuliiif,!' cmTt'tit, on flio ntlicr liiuul, clifckcil tin' tliiimiiij,' of tlir tiliii, 

 rotiirdi'il tlie fonuiitioii of colourt'd rinfrs if n])i)lit'd from tlit' bi^'iiiiiiiij.', and raiiidly 

 caused the disappcnranco of tlie hhick if nppiit'd afttT a vin;r of hhick liad alrt'adv 

 ln'cn foiinod. TIicm' etfccls wore niori' nuiikt'd witii tlit^ snap solution tiian witli 

 the ' hcjiiiihi plyct'iiijiie,' l)ut tlii' nntuio of tlie t'tU'ct ■was tlit» same with tin' two 

 liquids. 'J"he results arc valuahle, as ^iviufr the nii'aiiM of contrnllin^ tiio tliitniin|X 

 (if II film in oases wIuto it is dosirod to compare the properties of two films of 

 diiil-rent thickness. 



7. On fill' Ih'lf'itsion of Mcfidf. 

 Til/ rrofcssor W. Ciiandi,kk 'Kohehts, F.Ii.S. 



'->. Oil KiDiie Fhciioiiicna connected v.'ith Iron ami other }fetal,-i m the sultd 

 and molten sfiites, with notes of c.rperinicntf^-. JJi/ W. J. Mim,ar. 



( 1.) Object of Va }>(■)'. — I'eaults of experiments hy the author with various metals, 

 i<ii(,'h as cast-iron, p-iin-metal, phosphor bronze, lead, copper, and type-metal. The 

 Dbji'ot beini; to determine the cause of the veil-known phenonuMKm of the float- 

 ation of cold cast-iron on molten cast-iron, and as to whether any expansion took 

 [ilace upon solidification in the metals above noted. 



{'!.) Notes of some of the experiments from which the author concludes that 

 tlio cause of tloatntion of the solid metal on liquid metal of the same kind is 

 l)Wi\i(inrii, duo t(» expansion .suddenly set up in the immersed jiieies, and that this 

 expansion was fonndby careful measurement to be at least eqinil to the shrinkapo 

 or total decrease in length of the piece from white hot solid to finally cooled down 

 bolid. 



]'"urther, that the expan.sion observed is obtained -within much lower limits of 

 tfnn])eraturo than the shrinkafre ; as the piec(>s, -which were in all cases removed 

 trim tlie molten metal, innnediately on ai)peariiip: tloatinj^ liardly showed redness, 

 and when broken, it was found that the crystalline character of the metal 

 remained. 



(■"'..) Notes of experiments made l)y gradually heatinp pieces of cast-iron — the 

 ve>uUs of all these experiments leading the author to conclude that the rate of 

 expansion in cast-iron is at first much more rajiid at low temperature than after- 

 wards at high temperature. 



(4.) From experiments carried on with pieces of lead, copper, and type-metal 

 il was found that if any floatation occurred, it was only with .small light pieces — 

 lieavy pieces sinking and remaining at bottom of ladle. 



(Wm-metal and phosphor bronze behaved like cast-iron. 



(o.) Consideration of the peculiar appearance, or ' bipn!;.' observed on the 

 surface of molten cast-iron, the figures presenting a geometrical pattern, like inter- 

 lacing circles or stars. 



The author believes that this appearance is duo to cracks forming npon the 

 rapidly forming skin — these cracks taking more or less a circular form from tlie 

 convex forms, into -which the various parts of the surface aie thrown, due to the 

 bubbling up of gas or air. 



This appearance is limited to cast-iron, and experienced observers can ttU the 

 ([uality of the iron from the form of pattern or figures showing on the molten surface. 



(0.) From observation and experiments carried (jut from time to time, the 

 author concludes that no perceptiblo increase of volume of the metals noted occurs 

 at the moment of sclidification, at least when free from air or gas confined within 

 t.ho castinjr.' 



0. On the Velocity of Light of different Colours. 

 By Professor George Fori3es. 



i 



* See also Proceedings of the lioyal Society of Edinburyh, (session 1881-82. 



