260 Dr. Mac Culloch on the Annealing 



texture could produce a gray tint, such as is often found in 

 these defective metals. I call it a suggestion, because, 

 while engaged in these investigations, I was never able to dis- 

 cover any method of analysis by which the fact, if it be one, 

 could be ascertained. 



The suggestion is simply this, — that under the complete 

 liberty of crystallization permitted by high and long-continued 

 heat, an alloy is formed different from that which was intended ; 

 or that a certain definite combination takes place between the 

 tin and copper, so as to produce a mixture which is possibly 

 that of two alloys, or else is such as to set a portion of one or 

 other of the metals free, though of course under a state of 

 mixture which is unassignably minute. It is plain that this is 

 at best a probable state of things, while I need not say how 

 difficult the proof must be at present. It is probable, for this 

 reason : there is a crystallized metal or alloy, crystallization 

 takes place only in simple bodies or definite compounds, and 

 it would be very singular if the proportion of twenty-five copper 

 and twelve tin, which was my compound, should be that 

 definite compound, while as other proportions are used by Mr. 

 Ramage, such an occurrence cannot, plainly, happen in both 

 cases. And in defect of analysis, it has often seemed to me, 

 on the trial by acids, that there was more than one substance 

 in the defective and crystallized speculum, distinguishable by 

 the manner in which the acid acted on the surface. It might 

 not be very difficult to approximate to this point to a greater 

 nicety by the application of different acids, and by a subse- 

 quent examination of the proportions of tin and copper 

 dissolved ; but what I neglected to do when I had the power, 

 my state of health has long prevented me from following up. 



It seems unnecessary to add more on this part of the subject 

 in a paper so merely practical ; and if I ought now to show 

 how the annealing ought to be carried on so as to avoid the 

 evil in question, I find it very difficult to give such directions 

 as will enable any one to do as I have done in these cases 

 with success. And, indeed, it can scarcely be necessary; 

 since the general principle, and the cause of the evil having 

 been once explained, it will be easy for the speculum-maker 

 to apply what, after all, must be a matter of trial, and which 



