MOUNTING OBJECTS IN CANADA BALSAM. 213 



tuents which exists in the fresh Balsam ; and it is consequently 

 preferable to use in other ways the balsam which has become 

 somewhat too stiff, and to have recourse to a fresh supply of liquid 

 balsam for mounting-purposes. — In cases in which the Object might 

 be injured by the heat required to soften the Balsam, it may be 

 mounted in a solution of thickened Balsam in Chloroform, from 

 which the volatile solvent will evaporate in a few hours. This 

 solution should not be used until after it has stood for some weeks, 

 in order that its components may be thoroughly incorporated. — 

 When Canada balsam is to be employed as a cement, as for 

 attaching sections, &c, to glass-slides (§ 139), it should be in a 

 much stiffer condition ; since, if it be dropped on the slide in too 

 liquid a state, it will probably spread much wider and will lie in a 

 thinner stratum than is desirable. This hardening process may be 

 carried to any extent that may be desired, by exposing the Balsam 

 in an uncorked jar (the mouth of which, however, should be 

 covered with paper for the sake of keeping off dust) to a continual 

 gentle heat, such as that of a water-bath. 



159. In mounting Objects in Canada balsam, it is convenient to 

 be provided with certain simple instruments, the use of which will 

 save much time and trouble. — For the heat required, a Spirit 

 Lamp is by far the best source, both as admitting of easy regula- 

 tion, and as being perfectly free from smoke. — Where a number of 

 Objects are being mounted on the same occasion, it will be found 

 convenient to employ either a water-bath covered with a flat plate 



Fig. 99. 



Smith's Mounting Instrument. 



of metal, or a similar metal plate supported at such a distance 

 above the lamp-flame (§ 153) as not to become more heated than 

 it would be through a water-bath.* — For holding the slide whilst 

 it is either being heated over the flame or is being subsequently 



* Mr. Frederick Marshall has informed the Author that he has found 

 the following very simple apparatus extremely convenient : — A Water- 

 Bath made of tin, of such a size 'and shape as to afford a flat Stage for 

 laying the slide upon, and also to receive into its interior a wide-mouthed 

 bottle holding the balsam. If this Bath be filled with boiling water, the 

 balsam is liquefied without the risk of the formation of air-bubbles ; and 

 the slide also is kept sufticiently warm during the mounting process. 

 One supply of hot water will serve thus to mount from 12 to 20 objects. 

 By'marking on the Stage the outline of the slide and its "central point, 

 the right spot for laying the object upon the glass is indicated. 



