THE CONSTITUTION OF THE COPPER-TIN SERIES OF ALLOYS. 
39 
Sn 14. Chills at 780° and 772° (not reproduced). 
These were not very slowly cooled chills, consequently the alloy cooled too rapidly 
through the C temperature to allow of the complete absorption of the a. As a result, 
the ammonia etch shows a few very isolated dots of a on a white ground, and the 
FeClg etch shows large combs of jS symmetrically including the dots of a, the ^ 
being surrounded by a bluish-white tin-rich mother substance that was liquid at the 
moment of chilling. In tlie 772° ingot the imperfect transformation had the effect 
of depressing the temperature of complete solidification, for a v.s.c. chill at 775 
shows the alloy completely solid at that temperature. The effect of the suivival of oc, 
through too rapid cooling, is so well shown in the photograph of Sn 13 5 at 765 
(fig. 24), that we do not reproduce the Sn 14. 
Sn 14. V.s.c. chill at 775° (not reproduced). 
This, like all the chills of Sn 14, except granulated ones, is coated externally with 
a raised rectangular network of a or /3 combs, but the etched surface of the interior 
of the ingot shows no trace of combs. It is a compact mass of probably one crystal, 
containing no a. The striation in the ^ did not come at all leadily, seveial etchings 
and polishings having been made before it was noticed. This is quite free from a, 
and closely resembles fig. 23. 
Sn 14. S.c. chill at 766°, FeClg etch (not reproduced). 
A compact surface of striated No combs visible and no a. The chill at 740 is 
exactly similar. 
Sn 14. Chills at7lb° and 705°. 
Consist of 13 striated as before, with polygonal boundaries beginning to show, 
though they are not a marked feature and have to be searched for. The direction of 
striation changes abruptly at a boundary. 
Sn 14. Chills at 675° (fig. 29). 
We have two ; one a very slow cool (fig- 29). This contains only stiiated, but 
otherwise uniform, without polygonal boundaries or a trace of a. The other ingot is 
similar, except that there are a few specks of a, which is probably a commencement 
of the new crystallisation out of the solid that is so well marked in the next chill. 
Sn 14. Chill at 647°. NHg etch (not reproduced). 
This, at one end of the ingot, contains a few per cent, of the new a, but most of 
the surface is quite blank. No doubt, if etched with FeClg, thisdngot would have 
