B12 Scientific Intelligence. [April, 



presenting to it a piece of cold iron. 4. It effervesces in sulphuric 

 acid, and gives out abundance of muriatic acid. 5. When tlirown 

 into potasli ley, it gives out a strong smell of ammonia ; and when 

 the mixture is hciited, a strong efffrvescence takes place, and 

 ammoniacal fumes are given off" in abundance. These properties 

 leave no doubt that the salt is sal ammoniac. It is nearly pure; for 

 I find that it sublimes without leaving any other residue than a 

 slight trace of earthy matter. 



It is not easy to explain the formation of this salt. The coals 

 used as fuel would supply the ammonia; but I do not see any source 

 from which the muriatic acid can come. Perhaps Mr. Trimmer 

 him>elf may be able to favour us with an explanation, fioin his 

 Jinowledge of the su))stances mixed with the clay before it is made 

 into bricks. The subject is curious, and deserves investigation. 



V. Precession of the Equinoxes.* 



The Royal Academy of Sciences in Berlin had proposed, as a 

 prize, the most accurate determination of tlie magnitude of the 

 precession of the equinoxes. The pri/:e lias been adjudged to Mr. 

 Be>sel. No person could have performed this task witii more 

 fortunate success than Mr. Bessel, who lias been en>pIoyed for six 

 years in an examination of the Bradleian observations. During 

 these researches he made use of no fewer than 4585 observations 

 of the stars. VVe conceive we shall perform an acceptable service to 

 astronomers if we state the result he obtained of one magnitude, 

 which is daily used : — 



Luni solar precession = 50-35330"— 0-0002435890" (t — 1800): 

 General precession observed: 50-18924 + 0-0()024429G6" (t — 

 1800): 



Constant quantity by the precession in right ascension : 4601058" 



+ 0-0003590677'' (t - ] 800) : 

 Constant quamify by the precession in declination : 20 0496G" — 



0-0002135621" (t - 1800): t 



VI. Me/hod of ascertaining the Presence of Manganese. 

 I have been requested by a Correspondent, who subscribes himself 

 E., to inform him of a good test for manganese. He mentions 

 some unsuccessful results of his own to attain his object. I may 

 observe, in answer, that the colour of metallic jjrecipitants by 

 prussiate of potash, nutgalls, and hydrosulphurets, must always be 

 ambiguous when various metals hap'pen to be in solution together, 

 unless the experimenter possesses much practica] knowledge. I 



iqTi^*"'^ °'*'"^* '^ translated from the GottingiscJie gelehrte Anzeigenfor January, 



f \^^nl ?"''"'>' necepsary !o observe that t in tlie.^e formulas signifies the vear 

 of the Christian era. The nsults oblainctl by the French astronomers respecting 

 ihesevery quantities w iU be seen in (he account of the Institute in the ureseilt 

 fiiiOibenii thti Annals of Phitu sup hy. 



