<P> Chinese scientists of the Tang period employed complex chemical formulas for an array of different purposes, often found through experiments of alchemy . These included a waterproof and dust - repelling cream or varnish for clothes and weapons, fireproof cement for glass and porcelain wares, a waterproof cream applied to silk clothes of underwater divers, a cream designated for polishing bronze mirrors, and many other useful formulas . The vitrified, translucent ceramic known as porcelain was invented in China during the Tang, although many types of glazed ceramics preceded it . </P> <P> Ever since the Han dynasty (202 BC--220 AD), the Chinese had drilled deep boreholes to transport natural gas from bamboo pipelines to stoves where cast iron evaporation pans boiled brine to extract salt . During the Tang dynasty, a gazetteer of Sichuan province stated that at one of these 182 m (600 ft)' fire wells', men collected natural gas into portable bamboo tubes which could be carried around for dozens of km (mi) and still produce a flame . These were essentially the first gas cylinders; Robert Temple assumes some sort of tap was used for this device . </P> <P> The inventor Ding Huan (fl. 180 AD) of the Han dynasty invented a rotary fan for air conditioning, with seven wheels 3 m (10 ft) in diameter and manually powered . In 747, Emperor Xuanzong had a "Cool Hall" built in the imperial palace, which the Tang Yulin (唐語林) describes as having water - powered fan wheels for air conditioning as well as rising jet streams of water from fountains . During the subsequent Song dynasty, written sources mentioned the air conditioning rotary fan as even more widely used . </P> <P> The first classic work about the Tang is the Old Book of Tang by Liu Xu (887--946) et al. of the Later Jin, who redacted it during the last years of his life . This was edited into another history (labelled the New Book of Tang) in order to distinguish it, which was a work by the Song historians Ouyang Xiu (1007--1072), Song Qi (998--1061), et al. of the Song dynasty (between the years 1044 and 1060). Both of them were based upon earlier annals, yet those are now lost . Both of them also rank among the Twenty - Four Histories of China . One of the surviving sources of the Old Book of Tang, primarily covering up to 756, is the Tongdian, which Du You presented to the emperor in 801 . The Tang period was again placed into the enormous universal history text of the Zizhi Tongjian, edited, compiled, and completed in 1084 by a team of scholars under the Song dynasty Chancellor Sima Guang (1019--1086). This historical text, written with 3 million Chinese characters in 294 volumes, covered the history of China from the beginning of the Warring States (403 BC) until the beginning of the Song dynasty (960). </P>

Who acquired territories in central asia as the tang dynasty began to weaken