October, ’24] de ong: colloidal sulfur for red spider 533 
THE PREPARATION AND USE OF COLLOIDAL SULFUR AS A 
cCONTROL FOR RED SPIDER 
By E. R. deOng, University of California 
Abstract 
Two types of colloidal sudur have been prepared, (1) by running hydrogen sulfide 
into a solution of sulfur dioxid; (2) by precipitating lime-sulfur solution with acid. 
The former (hydrophilic collodial sulfur solution) shows the finest stage of division 
of sulfur particles. The latter (hydrophobic colloidal sulfur or precipitated sulfur) 
has a coarser sulfur grain which precipitates in a few days. The sulfur particles in 
both of the colloid forms are smaller than those of high grade dusting sulfur and hence 
oxidize more quickly, making them more active in the control of red spider than other 
forms of sulfur. Comparison of the toxic properties of the collodial solutions with a 
two per cent lime sulfur solution containing 0.6 per cent sulfur showed that the former 
were more effective especially at low temperatures. The addition of five pounds of 
ground or flowers of sulfur will probably prolong the length of time which such solu¬ 
tions would remain effective both as acaricides and fungicides. 
While testing the ovicidal action of lime-sulfur solution on the eggs 
of Bryobia praetiosa Koch, a few years ago, it was noticed that although 
but 50 to 60 per cent of the eggs were ever killed, yet the majority of the 
mites hatching from the treated eggs died within a few days. This 
work was done in the early spring w T hen the maximum temperature 
ranged from 50° to 65°F., temperatures at which ground or sublimed 
sulfur has little acaricidal effect. This led to the thought that the pre¬ 
cipitated sulfur (hydrophobic colloidal sulfur) from the lime sulfur 
solution was more active than the coarser forms of sulfur. Attempts 
made at this time to prepare sufficient precipitated sulfur or the hydro¬ 
philic form of colloidal sulfur for experimental purposes failed. De¬ 
velopments in the preparation and partial stabilizing of colloidal sulfur 
solutions have come rapidly in recent years. The great difficulty in 
handling such solutions is the tendency of the minute particles to aggre¬ 
gate or grow in size especially in the hydrophobic form. This is a serious 
criticism for the great advantage of such types of solution is the fine¬ 
ness of the particles. The use of a buffer type of colloidal solution such as 
glue or gelatine retards this tendency, but even then the hydrophobic 
form has largely precipitated out within a few weeks. 1 
The usual distinction made between a precipitated (hydrophobic) 
sulfur and a true hydrophilic colloidal solution is largely in the size of the 
particle. When first formed the colloidal particles show the Brownian 
movement and the majority of those which are visible under a low power 
1 H. C. Young. The Toxic Property of Sulfur. Crop Protection Digest Bui. 3. 
June 1923. 
