1S14.] Scientific Intelligence. 155 



be"-an to blow from the east, which dissipated the fog. It Increased 

 on Monday, Tuesday, and Wednesday, and occasioned a heavy fall 

 of snow. 



Nothing can be a more striking proof of the little progress hi- 

 therto made in meteorology, than the difficulty of proposing a legi- 

 timate explanation of a phenomenon so common and familiar as a 

 thick fog during winter. 



XI. Queries hj a Correspo?ide?it. 

 I have received the following queries from a correspondent, who 

 subscribes himself Inqtdsitor Imperitus, and who requests an an- 

 swer to them. 



1. Have any analyses been made of ancient mortars and cements ? 

 The absorption of carbonic acid cannot, as is said, be the cause of 

 their hardness and durability; at least, it remains to know what 

 favours the production of carbonic acid in mortar. For age, 

 which has produced that admirable degree of hardness in ancient 

 mortars, has irretrievably mouldered and crumbled the mortar of 

 other buildings not two hundred years old. 



ylnswcr. Ancient mortars have been frequently analysed, and 

 found to consist of nothing else than sand and lime ; and as good 

 mortar can be made in the present day as tlie ancient mortar. _ I 

 have seen houses 100, 200, 300, years old taken down, in which 

 it was easier to break the stones than the mortar. The treatise on 

 mortar by Higgins gives, I conceive, directions which would 

 enable any person to make excellent mortar, if he chuses to follow 

 them. Mortar owes its solidification not to the absorption of car- 

 bonic acid, but to the combination of water whh the lime. When 

 the lime contains clay, it even hardens under water, tiiough car- 

 bonic acid has no access to it. I have seen lime-water made 

 from a piece of ancient mortar ; a proof that it had not absorbed 

 carbonic acid at all. I do not know any thing of the history of 

 that mortar. The specimen was sent me froin Galloway in 

 Stoiland. 



2. What is the composition of Parker's cement ? 



Answer. If I recollect right, it is composed of clay iron-stone, 

 and lime, beaten together. But perhaps 1 am mistaken. 



.S. Is there any difference between sulphate and carbonate of 

 lime, when perfectly calcined? 



yhisutr. A very great ^lillerence. Carbonate of lime, by cal- 

 cination, parts with its carbonic acid, and is reduced to quick 

 lime. Sulphate of lime only parts with water, and still continues 

 a comj)ouiid of sulphuric acid and jinu,'. 



4. Wiiat is the menstruum of caoutchouc, and how are elastic 

 gum bougies formed ? Not certainly by welding one longitudinal 

 stripe to another, as is re|)resented ! 



Amwcr. The only known solvent of caoutchouc is ether vvaslied 

 in water. I liave no practical knovvledgc of the method of pre- 

 jniring bougici. 



