246 ^n Investigation of the Properties of Lactic Acid. 



degrees of saturation, 'f the lactic acid is digested with 

 the carbonate ot lead, it becomes browner than before, but 

 cannot be Juliy satarated with the oxide; and we obtain an 

 acid salt, which does not crystallize, but dries into a syrup- 

 like brown mass, with a sweet austere taste. When a so- 

 lution of lactic acid in alcohol is diiiesttd with finely pow- 

 dered litharce, until the solution becomes sweet, and is 

 then slowly evaporated to the consistence of honey, the 

 neutral lactate of lead crysialiizes in small gravish grains, 

 \vhich may be rinsed with alcohol, to wash off the viscid 

 mass that adheres to ihein, and will then appear as a gray 

 granular salt, which when drv is liiiht and silvery, like the 

 precipitate thrown down by alcohol from a precipitated al- 

 Kali. It is not changed in the air ; treated with sulphuretted 

 hydrogen, ii aff irds"pure lactic acid, if the lactic acid is 

 digested with a greater portion of levigated litharge than is 

 required tor its saturation, the fluid acquires first a browner 

 colour, and as the digestion is continued, the colour be- 

 comes more and more pale, and the oxide swells into a 

 bulky powder, of a colour somewhat lighter than before. 

 If the fluid is evaporated, and water is then poured on the 

 dry mass, a verv small portion of it only is dissolved ; the 

 solution is not coloured, and when it is exposed to the air, 

 a pellicle of carbonate of lead is separated from it. if the 

 dried salt of lead be boiled with water, and the solution be 

 filtend while hot, a great part of that which had been dis- 

 solved will be precipitated while it cools, in the form of a 

 white or light yellow powder, w hich is a sublaclate of lead. 

 This salt is of a \\s\\l flame colour; when dried, it remains 

 inealv, and soft to the touch, and it is decomposed by the 

 weakest acids, while the acid salt is dissolved in water, ex- 

 hibiting a sweet taste and a brown colour. When moist- 

 ened with water, it undergoes this change from the opera- 

 tion of the carbonic acid diffused in the air. If this salt is 

 warmed and then set on fire at one point, it burns like tin- 

 der, and leaves the lead in great measure reduced. A hun- 

 dred parts ot this salt, dissolved in nitric acid, and precipi- 

 tated with carbonate of potass, gave exactly 100 parts of 

 carbonate of lead ; consequently its component parts, de- 

 termined froiii those of the carbonate, must be 83 of the 

 oxide of lead, and 17 of the lactic acid. At the same time 

 we cannot wholly deperid on this proportion, and it cer- 

 tainly makes the quantity of lead somewhat too great. The 

 relation of the lactic acid to lead afl'ords one of the best 

 pjeihpds ot' recognising it, and I have always principally 



employed 



