102 INSECTICIDES, FUNGICIDES, AND WEED KILLERS. 



23. Hyposulphite of Soda, Na.S.PySHoO. — Preparation. — Sul- 

 phites boiled in presence of sulphur are converted into hyposulphites. 

 To accomplish this, a solution of sulphite of soda is lioiled with excess 

 of sulphur until saturated ; it is filtered and cooled. Large crj^stals of 

 sodium hyposulphite form. Commercially this salt is prepared by the 

 action of sulphurous acid on calcium sulphide (alkali waste). The 

 hyposulphite of lime formed is converted by sodium sulphate into 

 sulphate of lime and hyposulphite of soda. 



Properties. — Hyposulphite of soda is a colourless salt, permanent 

 in air, with a bitter taste and very soluble in water. It is less stable 

 in solution than in crystals ; even in the absence of air it is decomposed 

 into sulphite of soda and free sulphur which is deposited. In contact 

 with acids the hyposulphite is decomposed into fine sulphur and 

 sulphurous acid : — 



Na.SA + 2HC1 = 2NaCl + H.O + SO., + S. 



Heated out of contact w^ith air it splits up into sodium pentasulphide 

 and sodium sulphate. The use of sodium sulphite has been recom- 

 mended in medicine, especially against itch. Rubbing with a solu- 

 tion of hyposulphite of soda is followed by washing with dilute hydro- 

 chloric acid. The sulphurous acid disengaged and the sulphur pre- 

 cipitated in the pores of the skin make the sulphite a very efficacious 

 agent in the destruction of this acarus. 



Action on Plants. — The hyposulphite acts like the sulphite of 

 soda and sulphurous acid. Absorbed by the leaves of plants it is there 

 converted into sulphuric acid and burns the leaves. The experiments 

 therefore to replace sulphur by this salt w^hich, so to speak, contains 

 dissolved sulphur have been abortive because it burns the leaves, and 

 the more so the greater the heat. Kaserer observes that it suffices to 

 use a solution of hyposulphite rendered alkaline by milk of lime to 

 obviate this drawback. 



Action on Fungi. — Sulphur in hyposulphite of soda preserves its 

 anticryptogamic properties and imparts them to it. Like sulphur 

 hyposulphite of soda has been recognized as capable of killing all 

 fungi, the mycelium of which crawls on the surface of the plant. 



Puccinia Coronata, Cord, (coronated rust of oats). — Hitchcock 

 and Carleton examined the action of solutions of hyposulphite on 

 the uredospores of this rust and found that a 1 per cent solution has 

 no injurious action thereon, but it exerts a retarding action on the 

 germination and a diminution thereof on the seed steeped therein for 

 twenty-six hours. 



Uncinula Americana, How. (oidium of the vine). — Pauly examined 

 the action on oidium of a double hyposulphite of soda and silver. 

 After a microscopical examination he observed the great alteration 

 undergone by the mycelium in contact with a solution containing O'l 

 to 0-2 per cent of this salt, and concluded that the use of this salt as 

 a curative agent would give good results. However this salt, sold 

 under the name of " Puknos," has been abandoned in the treatment of 

 the vine because it burned the leaves especially during great heat, and 

 that much more so than the sublimed sulphur which it was to replace. 



